[ABSTRACT] IN SENDING out to the public this second and last of the two yearbooks on genetics and breeding, I would not want anyone to think that they complete the account of the efforts of plant and animal breeders in the United States. On the contrary, I would wish these yearbooks to be looked on as pointing the way toward a field of activity that will accomplish much more in the future than has been accomplished in the past. Life is always changing because environment is always changing. There are always new types of diseases, new insect pests, changes in soil fertility, changes in consumer demands. The work of the plant and animal breeders is directed to meeting these changes. It has only just begun. We have reached our present stage of development largely by rule-of- thumb methods; but discoveries not dreamed of a few years ago are being made, and they counsel greater boldness in experiment and promise closer control because they give us an increased understanding of the processes that go on in the minute cells where life has its beginning.
If genetics enables us to outdo nature’s own efforts, it is because it is in the truest sense a science of cooperation with nature. We want to do different things than nature does—for example, in the creation of hogs with plump hams or wheatgrass hybrids with plump seeds—but we have to learn nature’s methods of doing them. I think that more knowledge of how to cooperate with nature for our own good is the greatest need of the world today. Man’s control of his own future may depend in the long run on whether his biological knowledge, which is constructive, can catch up with his knowledge of the physical sciences, which has taught him so much about how to destroy.
WHAT THE BOOK IS ABOUT
Principal Research Writer, Office of the Secretary
This book rounds out the work of the committee on genetics appointed by the Secretary of Agriculture in 1933. The task set for the members of the committee was to make a national and to some extent an international survey of practical breeding and genetic research with those plants and animals that are important in American farming. The first fruits of the work appeared in the 1936 Yearbook of Agriculture as a series of papers dealing chiefly with the major crop plants and classes of livestock. The present volume covers an enormous and varied field, dealing with garden vegetables, northern tree and bush fruits, subtropical fruits, flowers, nut trees, forest trees, forage grasses and legumes, Angora and milk goats, turkeys, ducks, fur-bearing animals, honeybees, and finally that good friend of the farmer, his dog.
Many of the articles are unique in that nothing of a similar kind has been done in their field, and the two yearbooks together probably contain the most complete and up-to-date account of breeding work and genetic research in relation to farm plants and animals that can be found gathered in one place. Even in those cases where there is little work of a really scientific nature to report—and this is true in some instances, for scientific breeding is by no means universally applied as yet—the writer of the article has explored possibilities and endeavored to foresee fruitful lines of effort. Indeed, the possibilities of the future are necessarily a theme that runs through both books, because this science of genetics is relatively young, and much as it has accomplished in creating new forms of life better suited to the needs of man than the old, its greatest achievements undoubtedly lie ahead.
The genetics yearbooks, it may be said frankly, have something of the hybrid nature of much of the material with which they deal. They are intended for two groups: (1) Readers who want to know what is going on in the field of plant and animal breeding in order to enlarge their understanding and to enable them to carry on their farming operations more intelligently, and (2) students and others who have, or expect to have, a closer concern with the science of genetics. The latter group comprises scores of thousands of individuals, including young people now in schools and colleges who will be the American farmers and the agricultural scientists of tomorrow— some of them future leaders in shaping agricultural progress; a large number of workers in various parts of the country who are engaged in the practical effort to create better plants and animals; and teachers, extension workers, and others whose business it is to know as much as possible about all the major factors in modern agriculture.
To combine the interests of these diverse groups in a single volume is a difficult task, but judging from the generous reception given the last Yearbook, the results have at least been characterized by a certain hybrid vigor.
Another purpose also underlies this survey of breeding and genetics. It is an attempt to make a frank appraisal of the present situation on a major segment of the agricultural front—not only to sum up achievements, but to expose weaknesses and shortcomings. The reader of the 1936 and 1937 Yearbooks will admit that the short- comings have not been neglected. In almost every case, it is shown that we are far short of attaining the objectives that scientists believe we may attain with means as potent as genetics. As a matter of fact, though systematic breeding with such major crops as wheat has been going on for some time and has shown splendid results, it has only been begun in the last few years with many of the crops treated in the present book, and it has not had time to show what it can do. In other cases, the work is necessarily so slow that the results of the very earliest systematic efforts are only now beginning to be used. In the case of a new apple variety, for example, it takes nearly 40 years from the time the cross is made to the time when the variety is actually in commercial production. Tree breeders live in the present but think in the future.
On the positive side, however, there have been such outstanding achievements as the development of the wilt-resistant Marglobe tomato, which is now widely grown and saved the Florida producers from ruin; strains of cantaloups resistant to powdery mildew and of lettuce resistant to brown blight and powdery mildew—both of vital importance to California growers; snap beans resistant to some of the chief diseases that plague producers; cabbages resistant to yellows; sweet corn of such uniform and superior quality that it has remade canning practices; superior varieties of raspberries; blueberries far better than those produced by nature; a large number of improved navel oranges from bud selections; and many interesting new fruits created by hybridizing different kinds of citrus. Some of the new varieties and strains of plants developed by this constant activity are not yet quite ready for introduction.
Thus it is both heartening to discover how much has been accomplished and humbling to realize how little we know. There is probably not one writer of these articles who does not feel that the effort to sum up the past achievements and present status of the work in his field has been worth while. It has forced him to find out where we stand, to make a critical examination of what has been done, and to bring together many scattered fragments, so that their significance can be seen in the whole picture, including their relationship to the work of others in different fields. It would be well if a similar audit or stock taking could be made in other major branches of agricultural science, and, in fact, such a plan is now projected in the Department.
Much of the material was collected, as in 1936, through cooperative survey forms, or questionnaires, designed to survey the breeding and research work in all State agricultural experiment stations and in similar public institutions abroad. Private or endowed institutions, and even individuals, were included sometimes when it seemed that they might have valuable data. The information reported from institutions in the United States and Canada was in general considerably more detailed and complete than that from overseas, but in the latter case there was not always sufficient time to prepare complete data. A great deal of work was required in filling out some of these survey forms, and the Department heartily thanks all who cooperated.
The preparation of the papers was assigned to Department scientists actively specializing in work with each kind or group of plants or animals. The authors have drawn on their own experience and knowledge, and on the whole field of technical literature, as well as summarizing the information obtained from the cooperative survey of plant and animal improvement. The only uniform rule adopted for the papers was that the material of most interest to the intelligent farmer or the general reader was to come first and to be put in language as nontechnical as possible. The more strictly technical material was placed last. Thus, after the principle successfully followed by Jack Spratt and his wife, the general reader may skip the brief technical section at the end of most of the articles if he wishes, and the technical reader may skip the first part of the article if he is so inclined. Basic data and tables, including lists of plants with superior germ plasm for various characteristics available for future breeding work, appear in appendices to the articles.
Though the genetic background and breeding techniques are essentially the same with a good many different plants, it will be found that some discussion of these aspects of the work has been repeated to a certain extent. Since each such discussion is related to a particular organism, however, it seemed. best to let the repetition stand, partly for the benefit of readers who may be interested only in certain articles. Moreover, the subjects dealt with in the present book will appeal to a large number of gardeners, orchardists, bee- keepers, and other enthusiasts or specialists who may have only vague notions about genetics, even when they carry on practical breeding with the plants or animals in which they are most keenly interested. In such instances a certain amount of repetition should be useful in making the basic facts understandable.
Four articles in the last part of the book—which some readers may prefer to read first—deal in greater detail with some of these fundamentals. The science of genetics is not a particularly easy subject, though its broad principles are not difficult to grasp, and anyone who wishes to go very far in plant or animal breeding must be prepared to undergo some mental discipline-in the study of theory and technique if he expects to get all the facts straight. But for that matter, the details of the radio are not easy to grasp, either, yet there are thousands of capable radio amateurs who know a good deal about them. And in breeding work there is the advantage that the techniques involved, and the facts of genetics as far as they go, are at least relatively definite, which is more than can be said, for example, of the technique of writing good prose or poetry.
These concluding articles have been written with the lay reader in mind, but it will be found that they cannot be skimmed over like a detective story. On the contrary, they need to be read with the close attention that the detective in real life would give to some rather difficult technical evidence. For one of these articles we are indebted to A. F. Blakeslee, of the Carnegie Institution of Washington, who has been doing extraordinary things with the chromosomes of Datura, the genus to which our common jimsonweed belongs. Research in the field of unusual chromosome numbers is now attracting a good deal of attention among practical breeders because it suggests unique methods of creating new varieties and even new species of plants— that is, methods that are unique insofar as man is concerned, though it would seem that nature has used them from the beginning. For the chronology of genetics we are indebted to Robert Cook, editor of the Journal of Heredity, and to many of the leading geneticists and breeders in the United States, who critically examined his manuscript. E. N. Bressman has undertaken the difficult task of explaining some of the theory on which modern breeding practices rest; and J. R. Magness has dealt with the differences between vegetative reproduction and reproduction by seeds, which must be clearly understood in breeding work.
For a glossary of genetic terms the reader is referred to the 1936 Yearbook of Agriculture.
SUMMARY OF YEARBOOK ARTICLES
In the following pages all of the articles in the 1937 Yearbook are briefly summarized so that the general reader may quickly grasp the scope of the work as a whole.
In comparison with such major farm crops as the cereal, fiber, sugar, and forage plants, the vegetable crops are far more numerous, less understood genetically, and usually more limited to regional or national use. For example, superb English varieties of peas or cucumbers, or Italian varieties of tomatoes, either do not do well in this country or do not suit our habits and prejudices. In some countries American sweet corn is not considered fit for human food; and on the other hand, many vegetables commonly eaten in Asia are unknown in the United States. Vegetable breeding, in other words, is a highly localized affair. We draw on the whole world for variant plant forms, obtained by the Division of Plant Exploration and Introduction in the Bureau of Plant Industry, but today these are used almost entirely as sources of genes for specific characteristics needed to strengthen and improve our own favorite types.
Systematic vegetable breeding by public agencies in this country is for the most part not more than 10 or 15 years old—in some cases, very much newer. Prior to that time, for decades and generations individuals and commercial firms had been busy producing better vegetables, largely by mass selection, with a little hybridizing here and there. Naturally, we owe most of our present varieties to the work of these men. The number of improved new forms introduced by public agencies is as yet very small, though in acreage they make a more respectable total. They will steadily increase. The kinds of problems that are pressing today, notably the urgent one of disease resistance, and the increasing complexity of the research needed for quicker and more certain results make the old haphazard methods obsolete, excellent as they were in their time, and necessitate a well- organized scientific attack by public institutions. The commercial agencies in turn benefit by the work of these institutions. Seed certification in itself, though not directly connected with breeding, has been a State function of great value in holding the advances made by breeders.
Two new Federal institutions are of unusual interest and potential value. One is the United States Regional Vegetable Breeding Laboratory just established at Charleston, S. C., under the authority of the Bankhead-Jones Act of 1935. This is the only station in the United States devoted exclusively to vegetable breeding, and it will be concerned with basic problems affecting the Southeast. The other is the Great Plains Horticultural Field Station at Cheyenne, Wyo., where everything possible will be done to extend the meager list of vegetables now available for growing under the trying conditions found in this region.
There is a single appendix for most of the articles on vegetable breeding in the Yearbook, and this appendix includes work being done with some crops—sweetpotatoes and peanuts, for example—on which there was too little material to warrant separate articles.
As in the case of some of our literature and other native American products, Europe appreciated the tomato first, while Americans did not generally know that it was good to eat until about 1850, and the first improved varieties came from England and France. After 1870, commercial breeders in this country were active in selecting chance variants characterized by large handsome fruits, high yield, and plants adapted to local conditions. Among the leaders in this work was A. W. Livingston, of Columbus, Ohio. He and his associates were geniuses at selecting and perpetuating superior tomatoes. By 1910 there was a rich range of varieties, and the old methods are still used with some good results.
Chance variation is not certain enough, however, to meet the pressure of modern needs for resistance to disease, heat, and cold, and adaptability to long-distance shipment, new areas of cultivation, new Processes and uses. Since 1910, there has been a more systematic attack on these problems by State and Federal workers, and a greater use of genetic analysis and controlled hybridization to meet them. Major attention has been given to resistance to fusarium wilt, but nailhead rust, leaf spot, leaf-mold, mosaic, and curly top have all had some attention. Practically speaking, no research agency today would introduce a new tomato unless it was resistant to at least one very troublesome disease.
Many State stations have done and are doing notable work in this field, and the list of new varieties is growing to respectable length. Federal workers have also been very active. The most important variety of tomato in the world today, Marglobe, was developed by Pritchard and Porte in the Department. Marglobe is highly resistant to wilt under most conditions and to nailhead under all conditions, and it came in time to save the Florida tomato-shipping industry from ruin. But Marglobe has faults too, and it will be superseded by better tomatoes that will develop from the active research and experiment now going on.
Hot and sweet peppers, or chilis, also are native to tropical America. There has been comparatively little breeding work with these plants, and all the types grown today were known 200 or 300 years ago. A few enthusiasts among private breeders, however, have made improvements, particularly in uniformity, conformity to type, thickness of flesh, and earliness of maturity. The New Mexico and the Louisiana stations have introduced improved strains of hot peppers, and the Massachusetts and Connecticut stations have introduced early sweet peppers adapted to New England.
Even less systematic breeding work has been done with eggplant because of the relative unimportance of this crop in the United States. Native to the Tropics of the Old World, it has long been esteemed in some of the oriental countries. All the important varieties grown here were developed by private gardeners and seedsmen. The New Hampshire, Rhode Island, and Wisconsin stations are doing some breeding work for increased earliness, and the Central Experimental Farms of Canada have introduced an early productive strain of Black Beauty.
A rather impressive amount of research has been done on the genetics of the tomato, but there is a great need for the development of more accurate tests to measure degrees of resistance to disease as a foundation for working out the inheritance of resistance. More basic information of this kind is needed if practical breeding is to achieve results with greater certainty. Of great theoretical interest is the newer work on forms with abnormal chromosome numbers—both triploids and tetraploids have been produced artificially. There has been much less genetic and cytological research with the pepper and the eggplant. In the case of the eggplant, Japanese workers have made some interesting studies of hybrid vigor and parthenocarpic fruiting (without fertilization of the ovules).
Cucumbers and muskmelons are believed to have come originally from India and watermelons from tropical Africa. Pumpkins and squashes are of American origin. Columbus thoughtfully brought muskmelon seeds to North America, and in a few years native tribes from the West Indies as far north as Canada were growing melons. The early commercial and private breeders did their job so well with all these crops that some varieties originated over a hundred years ago are still popular among growers. Indeed, improvement by breeding today centers largely on fighting disease and spreading the climatic range of some of the cucurbits.
Cucumber growers suffer heavy losses from mosaic, downy mildew, and bacterial wilt. In the search for resistant varieties, plant breeders of the Department of Agriculture have found promising material among stocks from the Orient—China, Japan, India. Inbred lines of these show considerable resistance to mosaic and some resistance to mildew and wilt. Work is now in progress to introduce resistance into otherwise good American varieties by hybridization. At the Maine station, cucumber scab has received attention, and inbred lines pure for resistance, as determined by artificial inoculation, have apparently been found.
The story of the development of our numerous melon varieties from material drawn from many parts of the world is a complicated and interesting one. The most striking work in disease resistance has been in connection with powdery mildew, which suddenly became a menace in the Imperial Valley, the chief muskmelon section of the United States, in 1925. By 1928 J. T. Rosa of the California station and I. C. Jagger of the Department of Agriculture had discovered resistant plants in material from India. Commercially useless, they were crossed with good American varieties, then backcrossed to the American parent variety to improve quality, and a resistant hybrid, of which Hale Best is one parent, was ready for use by 1932: Further backcrossing to Hale Best and 2 years more of selection brought the still better Powdery Mildew Resistant Cantaloup No. 45 in 1936. The mildew threat in this area has been beaten. Resistant strains of Honey Dew and Honey Ball are now being developed.
The California station has recently developed superior watermelons from the old Klondike and Stone Mountain, and from Russian stock the Minnesota station has bred a watermelon that can be grown farther north than others. The most serious watermelon disease is fusarium wilt. Within the last few years, the Iowa station has bred a number of resistant strains, and in 1936 both the Florida and the California stations released new wilt-resistant watermelons. It is interesting to note that the first recorded attempt to synthesize a commercial plant resistant to a particular disease was a hybrid between watermelon and stock citron (wilt-resistant but inedible), made by Orton of the Department of Agriculture and produced in 1911.
Squash breeding has had rather different objectives—the production of varieties superior in uniformity, earliness, quality, and appearance. This has been done chiefly by isolating superior lines among varieties rich in variable characteristics—a task that is facilitated by the fact that inbreeding generally has no harmful effect on cucurbits (and, conversely, crossing apparently does not result in hybrid vigor). The Vermont station has been a leader in this work. The North Dakota station has produced a squash of high quality in an attempt to create a substitute for sweetpotatoes in the northern Great Plains area. The California station and the Connecticut station at New Haven have recently introduced new squashes.
Some inheritance studies have been made with all the cucurbits, and interesting work has been done on reproductive responses, breeding behavior, and pollination technique, in all of which there are peculiarities not common to other plants.
Varieties have a rather strict regional adaptability partly because they refuse to produce 100 percent normal bulbs except with a certain definite length of daylight. One group will do this with a short day of 12 hours. Another requires a 13-hour day, and another 13½ hours. Yellow Globe Danvers demands 14¼ hours of daylight, and Sweet Spanish strain no. 2 still more. Extra-early varieties, like Bermudas, will not do well when seeded in the North because the day has already passed the minimum bulbing length by the time seed is sown. Late varieties will not do well in the South because when the day is the right length for bulbing, heat, sunscald, pink root, and thrips retard growth. These conditions can be changed when breeders develop varieties resistant to diseases and insects and adaptable to a wider range of climatic conditions.
The principal troubles of onions are pink root, smut, mildew, smudge, neckrot, yellow dwarf, thrips, and bolting (premature seeding). Until recently, there was little or no attempt to overcome these troubles by breeding. Today the prospects look very promising. One of the most valuable aids in breeding for resistance to various troubles may prove to be the Japanese onion, especially the Nebuka type. Nebuka onions belong to a different species than our onions, and they are of very little use commercially in the United States because they produce no bulbs. But they are resistant to various diseases, insects, and adverse climatic conditions, and by suitable crosses, these qualities can be transferred to American types.
Active work is in progress now in the breeding of hybrids with Japanese onions that are resistant to thrips, pink root, and smut. Work is also in progress in isolating strains of onions resistant to mildew. Resistance to smudge, it has been determined, is due to a certain acid associated with the pigment in yellow and red bulbs; whether the genes responsible for this acid can be incorporated into white onions remains to be seen. A substance in the outer scales of colored bulbs also seems to be poisonous to the fungi that cause neckrot. The Sweet Spanish variety of onion has been found to be very resistant to the virus disease, yellow dwarf. Resistance to thrips shown by certain varieties and species seems to be due to growth habits and leaf shapes that fail to offer protection to the insects; perhaps there are also other characters involved that help the plants to withstand injury. Certain varieties have been found to be highly nonbolting, and these are being crossed to produce nonbolting hybrids. Indications are that the same thing may be done to secure resistance to freezing injury.
With such facts determined, the breeder is in a position to carry on a well-directed program. Techniques of inbreeding and cross-breeding are well developed. The onion is normally cross-fertilized, and selfing results in rapid deterioration, but with care it produces pure strains for hybridization. In making difficult species crosses—as with Nebuka—flies are specially grown and let loose in a cage that covers the emasculated seed parent and also contains a cut flower stalk of the pollen parent.
The onion has been used in interesting studies to develop methods of identifying specific chromosomes under the microscope, and there has been some genetic analysis of the inheritance of color and of certain abnormalities in chlorophyll development.
Peas apparently originated in Ethiopia, and according to one authority they are the only vegetable that can with certainty be traced back to the Stone Age. They are also the first crop with which controlled breeding was done to produce new varieties (by Thomas Andrew Knight, 1787), as well as the plant used by Mendel in determining the laws of inheritance that founded modern genetics.
They reached their greatest perfection in England, and many American varieties trace directly to the splendid products of the famous English breeders, beginning with Knight, who introduced the first sweet wrinkled pea. The most highly evolved variety so far is probably Laxton Progress, which blooms at the eighth or ninth node and is therefore a few days earlier than its nearest competitor, Hundredfold—a characteristic that, to pea farmers, was worth years of breeding effort.
American breeders received their greatest stimulus from the canning industry after 1900. Slight differences in such characteristics as pod size, pod curvature, tightness of peas in pod, number of peas in prime condition at one time, node of first bloom, and straightness of stem have been important breeding objectives to achieve the closest possible adaptation to machine handling and other needs of the industry. In garden peas, the chief American contribution has been a great reduction in the incidence of the defect known as “rabbit ear.” Today, preservation by freezing presents new objectives; and with all types of peas, American workers are now concerned with breeding for resistance to fusarium wilt and other diseases, as well as to insects and adverse weather conditions. Active breeding work is being carried on by several State experiment stations, notably Wisconsin, by the United States Department of Agriculture, and by some of the larger seed companies.
Elimination of strings was the chief objective of the early commercial breeders of snap beans, and the most successful among them was Calvin N. Keeney, of New York, who produced many varieties still popular, including Burpee Stringless Green Pod, Giant Stringless Green Pod, Stringless Green Refugee, and Brittle Wax. Later, the ravages of disease made it imperative to give major attention to breeding for resistance. New York State has led in breeding beans resistant to anthracnose. The Michigan, Idaho, and Wisconsin stations, the United States Department of Agriculture, and the Department in cooperation with the Wisconsin station, have produced varieties resistant to mosaic, and some of these are tolerant to bacterial blight. Strains resistant to bean rust have been bred by the Department and by the Virginia station. Thus the major bean diseases have been Overcome to some extent, and the work is being actively carried on to make greater gains.
Little controlled breeding work was done with lima beans until a Project was recently started in the Department. All the present Varieties resulted from selection. Of the two most extensively grown today—Henderson Bush and Fordhook (also a bush lima)—the former was found on a Virginia roadside by a Negro laborer in 1885 and sold originally to a seedsman in Richmond, and the latter was discovered growing in a field of pole limas in California in 1903. A hardy, high-yielding strain recently selected by the California station came from stock grown by the Hopi Indians.
Considerable genetic research has been done with peas, although this plant proved to be far more complex genetically than Mendel’s early work would have indicated. To date, 68 genes have been listed. Research in bean genetics has also been extensive, and the inheritance of disease resistance has received, and is still receiving, a good deal of attention. Very little genetic research has been done with the lima bean.
At least 4,000 years ago men were eating the leafy wild cabbage found on the coast of Europe and northern Africa; and this plant is supposed to be the original ancestor of such varied forms as the cultivated cabbage, cauliflower, broccoli, green-sprouting broccoli, Brussels sprouts, kale, collards, and kohlrabi. For our modern varieties of these vegetables we are largely indebted to farmers and to the assiduous work of commercial seedsmen, in both Europe and the United States, beginning in the late 1700’s.
The most important single achievement in modern cabbage breeding in the United States has been the development of varieties resistant to yellows (fusarium wilt)—an achievement that has saved growers from ruin in many sections and paid an enormous return on the cost. The problem was first attacked in 1910 in Wisconsin by L. R. Jones; and later J. C. Walker, of the Department of Agriculture, and his associates devoted many years to it. As a result of these intensive attacks, the wilt risk is now eliminated and there are yellows-resistant cabbage varieties of all the major types.
New varieties of cabbage that show improvements in other ways have been developed in Pennsylvania, Louisiana, and New York; and at several other State stations, as well as in the Department, breeding programs are in progress that promise worth-while results. The chief objectives today relate to diseases other than fusarium wilt, improved ability to hold up well in storage, better adaptation to particular localities, and a closer approach to consumer preferences, which favor a small or medium-sized hard head, mild or sweet in flavor, with crisp or succulent leaves.
Cauliflower and kohlrabi seed cannot be grown most successfully in this country, but broccoli seed can be, and new strains that mature at different times have been developed by private seedsmen in California. Green-sprouting broccoli has also been improved by breeding. New strains of Brussels sprouts have been privately produced in Oregon, and a new strain of kale has been released by the Virginia Truck Experiment Station. The Louisiana Station has introduced a new strain of collards.
One outcome of the breeding work with cabbage has been the development of interesting practical techniques for handling the plants and inducing the setting of seed under unusual conditions. Self-sterility is a problem with this plant, and as a result of intensive study much light has been thrown on the nature of self-sterility and self-incompatibility not only in cabbage but probably in other plants also.
Wide crosses between the cabbage and other species of the same genus have been fruitful in yielding cytological information, and there have been genetic studies of the cabbage concerned with the inheritance of characteristics of the leaf, the head, and the stem, as well as of plant height, bolting habit, season of maturity, and yellows resistance. Some work has been done on locating certain genes in definite chromosomes.
The turnip, rutabaga, radish, beet, carrot, parsnip, salsify, and taro are biennial plants, which means that they store a rich supply of food (mostiy starches and sugars) in their roots during the first season to support growth during the second season, when they produce seed. Early in his history man learned to take this food supply for his own nourishment, just as he learned to steal the store of honey from the bee.
Over a long period of time improvements were made and definite types were set in these root crops by crude selection. Even in our own times, practically no other kind of breeding work has been done with them. But though the results of mass selection have in some cases been excellent—as with the carrot—the method no longer meets modern needs. In particular, the attacks of diseases and insects make it imperative to develop resistant types by the newer methods of inbreeding, crossing, and the introduction of valuable germ plasm from wild forms of these species.
There is very little work of this kind to report. On the other hand, there has been some interesting genetic research with these plants, and the unusual difficulties that some of them offer in breeding technique have been ingeniously overcome. The road has been cleared to some extent for going ahead with practical breeding pro- grams based on definite objectives.
In order to "purify” the genetic make-up of a plant as a basis for combining desirable characteristics by crossing, it is necessary first to inbreed the plant. This is difficult in the case of some of the root vegetables. Turnips, rutabagas, radishes, and probably beets contain genes that make them sterile to their own pollen or pollen of certain other plants of the same variety. The mode of action of these genes has now been worked out. They are recessives and must be present both in the pollen and in the ovule to produce self-sterility. Their characteristics can be overcome to a considerable degree by applying pollen to a bud before it opens; or they can be replaced by “normal” genes through appropriate crosses; or naturally self-fertile lines can be discovered by enough searching and the others discarded.
In the case of the beet, the extreme dustlike fineness of the pollen, which can float in through tiny crevices, makes accurately controlled pollination difficult. This has been overcome by suitable techniques. The carrot was long thought to be self-sterile. Now it is known that the ovary merely develops before the pollen of the same flower is mature. Self-fertilization can readily be accomplished by using pollen from an older flower on the same plant. The flower parts are so minute that the usual methods of controlled pollination cannot be used, but this has been overcome by making flies do the work, inside special cages.
Along with such technical developments, research has uncovered facts about the inheritance of characteristics in these plants, some of which are of importance agriculturally—for example, bark and flesh color of turnip and rutabaga; color, corkiness, early and late flowering in the radish; color of root and top, and root shape in the beet; root color in the carrot. Investigation of chromosome behavior has also been fruitful. Certain wide crosses have been made, as between radish and cabbage, radish and Chinese cabbage, turnip and rutabaga, that may develop worth-while breeding possibilities.
Since the public became vitamin-conscious, the salad crops— lettuce, celery, endive, chicory, cress, and parsley—have increased in importance. Very little scientific breeding work has been done with any of these plants except lettuce and celery, the major salad crops. The production of both is confined to rather specialized areas. Lettuce, one of the oldest vegetables grown, came originally from India or central Asia and was introduced into the United States early in the colonial period. Celery, native to the Mediterranean region, was long considered to be poisonous and has been eaten only in modern times.
Lettuce breeders have. several solid achievements to their credit. Most notable of these is the development of the Imperial strains by I. C. Jagger, of the Department of Agriculture. This work was started in 1922 to meet the combined threat of brown blight and powdery mildew, which were on the point of wiping out growers in some of the largest western producing sections. The resistant Imperial strains, developed by hybridization, saved the industry in these areas.
Since transportation developments made possible the shipment of western lettuce to the East, eastern consumers have preferred the crisp western type. The present varieties of this type cannot be grown well in the eastern climate. A start was made in 1928 toward developing crisp-head. types for eastern growers, and the first of these, Columbia No. 1 and No. 2, were released by the Department in 1936. A wholly new type of lettuce, Cosberg (a cross between Cos or romaine and Iceberg) was also introduced in 1936. This is comparatively free from tipburn, which is very troublesome in the East. The Department is now cooperating with several eastern State stations for the development of other crisp types adapted to local conditions.
Tipburn and mildew are both serious in greenhouse forcing. The Ohio station has developed a tipburn-resistant strain of Grand Rapids, and the Massachusetts Station a butter-head type, Belmay, resistant to mildew.
Celery growers need earlier maturing plants and plants resistant to yellows, premature seedstalk development (bolting), and pithiness. Breeders have been attacking these problems. Michigan released its Michigan Golden Yellows Resistant celery in 1933 and its Curly Leaf Easy-Blanching (also yellows-resistant) in 1936. A new Non- Bolting Golden Plume has been introduced by a private seed concern in California. Pithiness has now been proved to be an inherited characteristic, which paves the way for breeding nonpithy strains.
Although lettuce flowers are difficult to handle in breeding operations, some genetic studies have been made on the mode of inheritance of various characteristics, including plant height, time of flowering, habit of growth, length, width, and area of leaves, and particularly color. Genetic studies in celery indicate that pithiness is due to a single dominant gene, and that bolting may also be a dominant characteristic controlled by several genes but greatly influenced by environment.
Some of the greatest advances in breeding technique in recent times have been made with field corn—in particular, the method of crossing certain inbred lines to produce a hybrid that has remarkable uniformity and productiveness. These advances have naturally been reflected in sweet-corn breeding also.
Two outstanding needs have dominated breeding work: (1) The canning industry requires stocks that are as uniform as possible in every way, besides having high yield. (2) The fact that sweet corn cannot be grown in the South, largely because of the ravages of the corn earworm and of bacterial wilt, makes it highly desirable to develop resistant varieties.
Breeders have met the first need so effectively with the newer types of hybrid corn that the canning industry itself has been revolutionized by the uniformity in texture and consistency of grains and the uniformity of ripening in the field. Whole-grain canned corn, frozen packs, and new machinery have been made possible by the work of breeders. About 80 percent of the yellow sweet corn grown for canning now consists of the newer hybrids, and about half of this is Golden Cross Bantam, a product of the Department in cooperation with the Indiana station. Other States that have led in recent breeding work have been Maine, Illinois, Connecticut, and Minnesota. Not the least of the advantages of Golden Cross Bantam corn is its resistance to bacterial wilt.
Promising work is in progress to meet the second major need— extension of the sweet corn region southward—by hybridizing sweet corn with the naturally earworm-resistant dent field corns of the South. The factors that make this dent corn resistant to the earworm have not yet been satisfactorily determined, but varieties developed from sweet- dent hybrids like Honey June and Surecropper Sugar have more resistance than any other sweet corn. Leaders in this work have been the stations in Texas, Florida, Georgia, and California. Truck and home gardeners in the South are keenly interested in these efforts.
The characteristic kernel composition of sweet corn, which distinguishes it from field corn, depends on a recessive form of the gene for starchiness. The presence of this recessive prevents the conversion of some of the sugar into starch. A good deal of work has been done On inheritance in sweet corn.
Popcorn pops because the horny endosperm in which the starch grains are embedded confines the steam generated by heat until it develops sufficient force to explode the kernel. Popcorns differ in popping expansion, and the differences can be easily measured. They also differ in tenderness and flavor of the popped kernels, productiveness, and resistance to diseases and insects. Fortunately high poppability and tenderness seem to go together, but unfortunately high poppability and productiveness do not, so that in breeding a compromise is necessary between these two characteristics.
Breeding work with popcorn has been relatively limited, but it has produced some promising results. Mass selection, based on actual popping tests or on a rough comparison of the amount of soft white starch in kernels (the more starch, the less popping expansion) is useful in bringing about a gradual improvement in popping expansion, at least up to a certain pomt. The improvement in a 6-year experiment conducted by the Department in cooperation with the Kansas station was about 36 percent, and the improved strain has been distributed as Supergold. Hybridization of inbred lines has been carried on by several stations. At the Minnesota station, 250 lines of a selection of Jap Hulless were developed by inbreeding, then culled to 7 lines by selection, and all possible crosses were made among the 7 lines. One cross was selected as superior; the hybrid, named Minhybrid 250, has had a 16-percent higher yield and a 29-percent higher popping expansion than the Jap Hulless used for comparison. A continuation of this project with new inbred lines is now in progress in Minnesota. At the Iowa station, a promising three-way hybrid is now under test, and a group of inbreds is in the developmental stage. In a cooperative project between the Department and the Kansas station, 81 hybrids have been produced recently, of which about one-fourth show some improvement in popping expansion, and almost 90 percent show a marked improvement in yield. The Michigan station is now carrying on an interesting experiment in producing synthetic varieties by combining a fairly large number of inbred lines.
Injury caused by diseases and insects is a distinct drawback in commercial popcorn. In the case of some diseases, selection for commercial characteristics tends also to bring about some selection for resistance. In the Southern States particularly, damage from the corn earworm and from storage insects is serious. The Texas station has a project under way in which an attempt is being made to introduce the insect resistance of their adapted field corn varieties into popcorn of good popping quality.
Native to cool regions in South America, potatoes were taken to Europe by early Spanish explorers and grown there for a hundred years before they were introduced into the New England colonies from Ireland (1719, Londonderry, N. H.).
For another hundred years, little improvement was made in varieties. Then there was a rush to produce better potatoes. A minister, Rev. C. E. Goodrich, of Utica, N. Y., laid the foundations for potato breeding. He thought the ravages of late blight were due to loss of vigor through long vegetative reproduction by tuber cuttings, and he proposed to restore vigor by growing plants from seed. Some 170 varieties can be traced back to a single one of his seedlings, Garnet Chili. C. E. Pringle, of Charlotte, Vt., was the first to make systematic attempts to obtain seed by controlled hybridization.
In the United States today, potato breeding is extensive and well organized under a national potato-breeding program. Under this program, the Department coordinates the work in 13 States that are carrying on active breeding projects, with 21 States cooperating in testing worth-while material developed in these projects. Regional problems are considered, and States in which seed cannot be grown obtain it from States in which it can be grown. The various Department field stations and State agricultural experiment stations stress different aspects of the general problem, but altogether practically every aspect of potato breeding receives attention, including disease resistance, yield, adaption to locality, earliness, tuber shape, smoothness (depth of eye), cooking quality, breeding methods, genetic analysis, and study of chromosomes.
The breeding methods include the full range of those used in modern plant breeding—the introduction of new varieties or species, selection of colonal lines, crosses between. varieties, brother-sister crosses (sib-mating), backcrosses to parents, selfing and the recombination of selfed lines (as in the breeding of hybrid corn), outcrossing to unrelated strains, the synthetic building of strains by a combination of various methods, and wide crosses between different species (as between a cultivated and a wild form).
The outstanding problem is resistance to diseases, including a whole group of virus diseases, late blight, common scab, fusarium wilt, rhizoctonia, early blight, blackleg. These diseases add enormously to growers’ costs. Late blight, the most important, has caused losses of 9,000,000 bushels of potatoes a year for the last 10 years; in 1928, the loss was 28,000,000 bushels. The severest possible tests for resistance are given, and so far very promising progress has been made in the development of many varieties resistant to late blight, a large number resistant to scab, a large number resistant to mild mosaic, and one variety and several of its progenies immune from latent mosaic. The search for disease resistance will be continued until every possibility has been exhausted.
From a practical standpoint, six new varieties have been named and distributed in the last 5 years (Katahdin, Chippewa, Golden, and Houma by the Department; Warba and Red Warba by the University of Minnesota). other, not yet named, is being tested by farmers. Katahdin and Chippewa are now firmly established as commercial varieties.
With a wealth of available breeding material, breeding methods well tested, considerable genetic and cytological information, and a planned cooperative program, potato breeders are in a position to expect further progress with confidence.
The strawberry is not of ancient lineage as a cultivated fruit, though the Indians of Chile were growing remarkably fine selections of the wild beach strawberry before the time of Columbus. Five plants of this type reached France in 1714, and these were crossed with the wild meadow strawberry of eastern North America, which had previously been taken to Europe. The result was a vigorous hybrid, the modern cultivated strawberry—a European creation out of American parentage, so welcome and adaptable that it is now grown from Alaska to New Zealand.
Since the strawberry is relatively so new, most of our varieties are products of breeding, though a few have been found as chance seedlings in the wild. These are natural hybrids of cultivated and wild berries, for many of the wild sorts now contain chromosomes obtained from the pollen of their cultivated neighbors. Extensive commercial production did not begin until after the Civil War, when the first firm-fruited variety, Wilson, made strawberry growing in the South possible. Today, 20 varieties created in the last 45 years (Gandy, the oldest, in 1885) account for over 99 percent of the total acreage, and 6 of these (Klondike, Howard 17, Aroma, Blakemore, Missionary, and Marshall) for 78 percent. Most of the 20 varieties were produced by private breeders, and several famous private breeders of outstanding varieties are still living and carrying on their work.
Systematic strawberry breeding is now being carried on by the Department and by the agricultural experiment stations in 26 States, as well as in Alaska and Hawaii. Hundreds of thousands of seedlings are constantly being grown, of which perhaps two in a hundred are selected as worthy of a first fruiting test, and a very small percentage pass the final rigid test and are named and introduced. At many of these stations the work is new and has not yet had time to produce results. The Department has released 7 varieties, Minnesota 16, New Jersey 1, New York 21, North Dakota 1, Oregon 1, South Dakota 2, Tennessee 1, and Alaska 1. Strawberry growers readily adopt improved varieties, and such new introductions will account for an increasing acreage in the future. Breeding work is also actively carried on in Canada, England, Norway, Sweden, Germany, Switzerland, Czechoslovakia, the Union of Soviet Socialist Republics, Japan, and Australia.
The usual method of breeders is to cross varieties and species and backcross to the parents. The newer method of inbreeding and combining inbred lines has been used very little, partly because the strawberry plant loses vigor so rapidly with inbreeding. This method will very likely be necessary, however, to eliminate recessive genes that probably account for susceptibility to certain diseases as well as for other weaknesses. There is considerable confidence today that the excellent characteristics of many varieties and of the three wild 56-chromosome species (meadow strawberry, beach strawberry, Rocky Mountain strawberry) can be combined in a few outstanding types suitable for the wide range of strawberry-growing regions. Broadly, the objectives today are greater resistance to several diseases, and possibly to insects and nematodes; greater resistance to high temperatures, low temperatures, and drought; better adaptation to long and short days; better dessert quality under adverse weather conditions; increased firmness and toughness of skin; and better adaptation to certain specific uses such as canning, preserving, freezing, and flavoring.
Fundamental research with the strawberry has been concerned with the inheritance of a few contrasting characters and with chromosome behavior, largely in crosses between species with different chromosome numbers.
By clearing the forests, Americans set up a vast natural blackberry breeding project, for in the clearings the sparse growth of blackberries became dense, and since all blackberries need cross-pollination, a multitude of natural hybrids arose. For the last 75 years or so we have been making selections from this pool of mixed germ plasm, which has been the source of almost all our commercial varieties, including Lawton, Eldorado, Snyder, and the dewberry or trailing blackberry Lucretia. However, in the West the Logan (Loganberry) came from a cultivated variety, the Young dewberry (Youngberry) is an artificially produced hybrid, and the Evergreen (Black Diamond) and the Himalaya are of European origin. Whether the Logan is a blackberry-raspberry hybrid is still in dispute.
Comparatively little systematic breeding has been done with blackberries by public agencies, but the Department and several of the State stations are doing some work. There is much interest in developing thornless varieties. This has been accomplished several times by the use of mutations, but unfortunately only the outer layers of the plant tissue carry the characteristic of thornlessness, and new plants developing from the inner layers—as they do in the case of root cuttings—are all thorny. Also, thornless plants generally tend to be sterile. Other major practical objectives in breeding are superior hardiness, productiveness, vigor, flavor, firmness, and size; smaller seeds; and resistance to diseases, nematodes, and drought. Many crosses have been made by the Department and by the New York, Rhode Island, and Texas stations, and a few improved varieties have been introduced as a result. Workers at the Texas station, and in England, have been especially interested in experimenting with blackberry-raspberry crosses, but none of these has as yet produced a worth-while commercial variety.
Both European cultivated red raspberries and selections from native wild varieties were probably grown in the United States before 1800, but the red raspberry did not become commercially important until after 1865, when an industry was founded on the famous Cuthbert variety, discovered as a chance seedling in New York. The best cultivated red raspberries were developed by definite breeding work, mostly by the State stations, far more than has been the case with blackberries, and since this work began a considerable number of Superior varieties have been introduced, including such important ones as Latham, Chief, Ohta, King, and Viking.
Breeding work is being actively carried on by the Department and the experiment stations in New York, South Dakota, Illinois, Washington, Minnesota, Tennessee, and North Carolina, and many thousands of seedlings that have resulted from crossing and selection are being tested. This includes work with the black and purple raspberries, crosses between red and black and between American varieties and Asiatic species, and the development of fall fruiting or everbearing forms and of varieties adapted to special purposes. Among other results are the production of berries bigger than would have been thought possible 10 years ago, and considerable success with varieties able to resist or escape major diseases.
But there are still great possibilities for improving the red raspberry, notably by bringing together in a single combination some of the superior characteristics now found separately in cultivated American and European varieties. Moreover, a large number of wild varieties exist in Asia and elsewhere, with extremely varied characteristics of plant and fruit, that the breeder has hardly yet begun to use in his programs. New possibilities will undoubtedly develop as these are more systematically explored.
White-pine blister rust is not passed from pine to pine; it goes from pine to currant or gooseberry and then back to pine. This is unfortunate for currants and gooseberries; they have had to be wiped out in a good many places to save the pines. Extension of the now greatly reduced acreage will depend largely on the development of resistant varieties.
There are two kinds of currants, red and black. Of the red currants, five species, native to Europe and Asia, are considered especially important for breeders, and most of the leading American varieties (Fay, Wilder, Red Cross, Diploma, and Perfection) came from two of them. These American varieties were developed between 1877 and 1887 out of material that had been coming from Europe almost since the first settlement of New England. The European black currant is useless for this country because of its high susceptibility to blister rust, but the American black currant—which also has golden or white forms—is more resistant. Four improved American black varieties (Tonah, Atto, Mato, Wanka) were introduced by the South Dakota Station in 1925.
Very little systematic breeding work has been done with currants by either State or Federal workers. The South Dakota station has worked with black varieties; a number of crosses have been made and are being studied in New York; Minnesota has recently introduced a red selection, Red Lake; and Federal workers have made some crosses and selections but have introduced no varieties as yet. The most promising rust-resistant variety is Viking, an introduction from Norway. It seems in fact to be immune and is now being extensively tested by the Department cooperating with State stations. There are promising possibilities in breeding work with currants, especially the hardy, drought-resistant, vigorous American black varieties.
Greater promise, however, lies in the work with gooseberries. The greatest development of this fruit has been among the English, who became connoisseurs of gooseberries, held gooseberry shows, and offered prizes that stimulated breeding work, especially for large size. In the United States, gooseberry growers were discouraged by mildew until after 1900, when fungicides were used to controi the disease. The most important gooseberry in this country has been Downing, a mildew resistant variety introduced about 1855. Poorman (1896) is the largest American-European hybrid. About a dozen species native to the United States are promising for breeders. They have a wide climatic range and such valuable characteristics as resistance to mildew, leaf spot, and high summer temperatures. These characteristics need to be combined with the great size, fine flavor, and attractiveness of European varieties, and some of the hybrids developed show the possibilities.
Breeding work has been carried on by several State stations. The South Dakota station has made crosses between a native wild species and European varieties, and these have resulted in some dozen introductions. The North Dakota station has recently introduced three varieties from crosses and is studying the inheritance of important characteristics. The New York station at Geneva has introduced one variety, and the Minnesota station has introduced an improved variety. The Illinois station is working for greater production, larger size, higher flavor, fewer thorns, and resistance to leaf diseases. The Department is doing some selection and hybridization, and has recently introduced one gooseberry, Glenndale, adapted to the upper South.
The breeding of both currants and gooseberries has been actively carried on in Canada, and in England research work has proceeded far enough so that the use of X-rays to induce mutations is now being studied. Breeding work is also being done in Sweden and in the Union of Soviet Socialist Republics.
All cultivated plants came originally from the wild, but only the most outstanding or the most adaptable have been extensively grown by Man. Others from which men gather food might be adapted to cultivation and improved by breeding, just as the wild blueberry has been adapted and improved in recent years. Among the plants useful for landscaping there are also a number that might yield new forms or be made more valuable in other ways, if breeders would give them systematic attention. For example, columnar deciduous trees other than the Lombardy poplar might be created by breeding and would be extremely useful.
A few ornamental plants whose fruit is promising as food have received some attention. The actinidias (Chinese or Japanese gooseberries) are climbing shrubs bearing fruit up to the size of an egg, with a texture like that of a fresh fig, edible fresh or as a jelly or a cooked sauce. A single vine may produce several bushels of fruit in some years, but the need is to develop types that will bear regularly. The American cranberrybush or highbush cranberry (a close relative of the elderberry) produces fruit that makes a highly colored jelly of strong flavor. Several State experiment stations have cooperated with A. E. Morgan and the Department in improving this fruit by breeding, and three varieties are now available commercially. The goumi, or Eleagnus, has a tart fruit that is good in sherbets and is of considerable importance in central Asia. The plant is hardy and drought-resistant and might well be improved by breeding. The fruit of the oriental or flowering-quinces (Japanese quince is a common form) is extremely useful for jellies and preserves in combination with other fruits because it is rich in pectin and contributes an agreeable acid flavor. By breeding, it should be possible to develop larger fruit, with more acid and pectin and better color, which would be of great value in the preserving industries. The Chinese bush cherry (Manchu or Nanking cherry) is now receiving attention for its fruit, which has an attractive tang and an agreeable range of flavors and textures. This fruit too has commercial possibilities, and some breeding work has been done with it in Iowa, New York, and Massachusetts.
Only a short time before his death on January 9, 1937, Frederick V. Coville completed an article for this Yearbook describing his work in developing the cultivated blueberry from the wild blueberry. Dr. Coville served 49 years in the Department of Agriculture, and probably his work with blueberries will stand out as the most important achievement of a fruitful career. It founded a new and thriving industry.
The work began in New Hampshire in 1906 with a study of the fundamental facts in the life history of the wild blueberry. The first fact established was one not before known—that blueberries, rhododendrons, azaleas, the mountain-laurel, and many other plants require acid soils.
Next, methods of grafting, budding, division, layering, propagation of twig cuttings and root cuttings, and pollination were worked out.
Then plants with superior fruit were chosen for breeding experiments. The first one, a highbush blueberry found in a pasture in Greenfield, N. H., was named Brooks. To the excellence of this first berry, Dr. Coville attributed much of the success of many of its later descendants. Efforts were made to self-polinate the Brooks, without success, and after other attempts, this method was abandoned in favor of cross-pollination. Much later, it was found that in cross-pollination, chromosome numbers were all-important. Even distantly related plants with the same number of chromosomes would cross, but if they did not have the same chromosome numbers, the cross yielded no fruit.
The second wild blueberry chosen was Russell, also from New Hampshire. In 1911 this was crossed with Brooks, and some of the first-generation hybrids were crossed with each other. Among 3,000 second-generation progeny, there was much segregation for various characteristics.
Thereafter, Dr. Coville made an intensive search for superior wild berries, enlisting the cooperation of Elizabeth C. White, of New Lisbon, N. J. Up to the year 1936 about 68,000 pedigreed blueberry seedlings were fruited and carefully tested for superior characteristics of bush, size of fruit, ease of picking, size of scar when picked, size of calyx, keeping quality, firmness, tendency to crack, and flavor. Taste tests were especially exacting and, with the consumer in mind, Dr. Coville would release no variety, no matter how remarkable its size or how good its other commercial characteristics, unless its flavor met his standards.
The largest berry developed in this work had a diameter of more than 1 inch, but it was not released because of inferior flavor. A hybrid between this and the finest-flavored berry, Stanley, has so far reached a diameter of nearly 1 inch. It is not yet ready to release, but Dr. Coville named it Dixi. His article describes the characteristics and ancestry of all his improved varieties—Pioneer, Greenfield, Cabot, Katharine, Rancocas, Jersey, Concord, June, Scammell, Stanley, Redskin, Catawba, Wareham, Weymouth, and Dixi.
To evaluate a new apple variety takes 25 years from the time the cross is made, and another 5 to 15 years will elapse before it is in commercial production. Practically speaking, the apple breeder works for his descendants, not for his own generation. Therefore as yet few of our widely grown varieties are the result of systematic hybridizing, even though this work was under way in 1895. Most of them came from superior chance seedlings. Apples were brought over from Europe by the early colonists, the seeds were widely disseminated, and since apples do not come true from seed, the range of differences in tree and it was very great. In fact this process extended back into early times. Primitive man appreciated the wild apple, though it was a wry thing, and he early began selecting and cultivating it. Budding and grafting were practiced over 2,000 years ago.
Today we need fruit with quite definite superior characteristics, and the hope of obtaining it lies in the extensive breeding programs of the present and the future. What are the objectives? Increased winter hardiness, of first importance in northern regions; disease resistance (the major diseases are scab, blotch, bitter rot, fire blight, and apple cedar rust); resistance to spray injury; late blooming to escape spring frosts in some sections; a combination of rich-flavored fruit with desirable tree characters (disease resistance, etc.); a greater range of fruits with high color and quality combined with ability to keep well in storage; varieties adapted to the far South—at present there are none that are satisfactory.
There is sufficient variation among the many different kinds of apples to give assurance that many of these desirable characters can brought together in new varieties.
Three methods are available to bring about these improvements:
(1) Keeping a careful watch for bud mutations; this has been practiced rather intensively during the last decade, and some very superior strains have resulted. The method is still highly promising, though it is limited to a relatively narrow range of improvement among existing varieties. (2) Hybridization to produce really new varieties by combining different characteristics. In some cases it is possible to go rather far afield; hardy crab apples are being crossed with commercial varieties of apples, for example, to get extreme cold resistance. (3) Producing varieties with unusual chromosome numbers. It happens that about 25 percent of our commercial apple varieties are triploids—that is, they have three full sets of chromosomes in their body cells instead of the normal two sets. Always these triploids have unusually large fruit and a vigorous type of tree; that is why so many of them happen to have been selected as superior. But the occurrence of triploid apples is very rare in nature, and so far it has been impossible to create them by controlled breeding methods. This is a secret that the apple breeder is trying intensively to solve.
Breeding projects are under way at the experiment stations in several varieties, and tens of thousands of seedlings are under test. So far, Iowa station has introduced 13 named varieties; Minnesota, 5; Missouri, 7; New York, 15; South Dakota, 17. Work is also in progress in Idaho, Illinois, Maine, Maryland, Massachusetts, Ohio, and Virginia, and the Department is doing a limited amount of breeding. A major program has been carried on in Canada, and apple breeding is combined with the breeding of other fruits in several European countries.
Europeans have the same fondness for pears that Americans have for apples, and a great many delicious varieties have been developed in Europe. A Belgian physician, Von Mons (1765-1842), had as many as 80,000 seedlings in his gardens and developed over 400 varieties. At least as early as 1794, however, pears in the United States met the nemesis that has dogged them ever since. This is fire blight, a bacterial disease that attacks roots, crown, trunk, limbs, blossoms, and fruit. It is ruinously virulent in most of the East; in the West, relatively cool dry summers make it less destructive; but even there, it is a source of great trouble and expense to growers, since the only known method of control is by careful surgery.
Thus the fire blight menace dominates pear breeding in the United States. The European pear, source of all the fine-fleshed, buttery, melting, aromatic varieties such as Bartlett, Anjou, Bosc, and Winter Nelis, is especially susceptible. The Chinese or sand pear, coarse, gritty, and inferior, is resistant. Around the middle of the last century, hybrids between the European and the Chinese pear began to appear—Le Conte and Kieffer, for example. Although these are inferior in quality, they are about the only pears that have enough blight resistance to be grown in most parts of the East. One pear apparently of straight European parentage, the Seckel, is also resistant.
The problem, then, is to develop a wider range of the superior European varieties with resistance to the disease, either by hybridization or by selection. The most important basic breeding material includes the European pear (generally susceptible but with occasional resistant forms), the snow pear of southern Europe (susceptible), the Chinese or sand pear (variable resistance), the Ussurian pear of China and Siberia (very resistant, and especially valuable because the quality is fair), the Callery pear of China (resistant), the birchleaf pear of China (variable resistance). There is enough range in the available material to meet all requirements, including superior winter hardiness, which is needed in some parts of the country; but it may be another hundred years before the problem of fire blight is really solved, considering the length of time it takes to test a single generation of tree fruits.
The Oregon Station has led in this work. There F. C. Reimer has tested the resistance of practically all known species and varieties of pears, and of many hybrids, using artificial inoculation as well as natural infection. One of the most valuable breeding stocks is a highly resistant Anjou seedling called Farmingdale, found accidentally on a farm in Illinois. Ten other very resistant Eurpoean pears have been found in 10,000 seedlings, and all transmit a high degree of resistance in crosses.
The Department has also carried on fairly extensive breeding work for blight resistance, and 5,000 seedlings, inoculated each year, are now being grown to fruiting. Work has also been done in California (for range of ripening season), Georgia (studies of resistance), Iowa winter hardiness), Maryland, Michigan, Minnesota, New York (primarily for high quality and long ripening season), and Tennessee. Some new varieties have been introduced as a result of this work.
A limited amount of work has been done on the cytology and genetics of pears, but inheritance studies are difficult because selfing is impracticable in most varieties.
Obedient to official urging and command, the early colonists in the eastern United States planted grapes of the traditional fine European varieties. All of these ventures failed miserably; the European varieties could not stand the diseases, the insects, and the cold that faced them in this part of the new land. In California, however, they throve ever since they were introduced by Mission Fathers from Mexico in 1769, and after 1850 grape culture in that State grew with great rapidity. Meanwhile, tardily, easterners began to become aware of the value of their own native grapes, which grew abundantly in the wild. Three chance seedlings—the Cape (believed to be identical with Alexander), discovered in 1806; the Catawba, first propagated in 1819; the Concord, named and introduced in 1854—had sufficient merit and popularity to turn the attention of breeders to these native species. Thereafter several men did notable work in selecting native varieties and hybridizing them both among themselves and with European grapes. Outstanding among these early workers were E. S. Rogers (Agawam), A. J. Caywood, Charles Arnold of Canada, G. W. Campbell (Campbell Early), Louis Suelter (Beta), J.H. Ricketts (Downing), and T. V. Munson, who originated more hybrids than any other man in the country.
Thus American grape growing has had two distinct lines of development. On the Pacific coast (especially in California), where 90 percent of the commercial grape culture is centered, European varieties are grown for the production of table grapes, raisin and currant grapes, and wine grapes; throughout the rest of the country, native varieties, hybrids between these, and hybrids with European varieties are grown for table grapes, wine grapes, and unfermented-juice grapes (the foxy flavor of the Concord, which is a fox grape, is important for this last use). Even the European grapes in California, however, must be grafted on native American rootstocks, which alone are resistant to phylloxera, an American insect that, finding its way to Europe, compels European growers also to use American grapes as rootstocks.
Grape breeding is actively carried on by the Department and by the State agricultural experiment stations in California, Georgia, Maryland, Minnesota, Missouri, New York, South Dakota, Texas, and Virginia. Many thousands of seedlings from an immense number of crosses are being grown and tested, and improved varieties have been released by the Georgia, the New York (Geneva and Fredonia), and the South Dakota stations. The general objectives in this work are improved fruit quality, disease resistance, and local adaptability; but there are separate objectives for the three main types of grapes. Thus, for American native bunch grapes it is desirable to have larger clusters and berries; some of the rich vinous flavor of the European grape; more edible skin, more melting flesh, seeds more free from the pulp, increased sugar content. For the native muscadine grapes of the South, it is desirable to have larger bunches, better adherence of berry to stem, more tender skin, better flavor, smaller seeds. For the European grapes, it is desirable to have among the table types, more seedless varieties and a larger assortment of black, red, and white grapes ripening from early to late; among the raisin types, several improvements to meet specific needs; among the wine types, improved flavors (perhaps a blend of several flavors for certain kinds of wine), juice of better color, vines resistant to phylloxera to eliminate the necessity for grafting.
Needless to say, grape-breeding work is also being actively carried on in foreign countries, notably France, Germany, Italy, Czechoslovakia, the Union of Soviet Socialist Republics, and Australia.
Genetic analysis is slow, and there is need for more information on the inheritance of characters of importance, especially resistance to diseases.
Grown in China thousands of years ago, the peach early spread throughout Europe and was brought to North America by the colonists; but commercial growing did not begin here until the nineteenth century, when orchards propagated from cuttings were first established. Between 1850 and 1900, peach growing became highly specialized, and to meet the need for types suited to different regions many varieties were developed by seedling selection, including such present stand-bys as Hale Early (1850), Belle and Elberta (1870), Crosby (1876), Champion (1880), Carman (1889), Rochester (1900).
Today, systematic breeding by hybridization is conducted by the Department of Agriculture and by the agricultural experiment stations in California, Illinois, Iowa, Maryland, Massachusetts, Michigan, New York, New Jersey, Texas, and Virginia, as well as in Canada. Many of these have only started recently, but the Department has introduced 4 varieties (1935), New Jersey 18 (1925-34), California 1 (1933), Iowa 1 (1932), Michigan 1 (1932), and Canada 6 (1925-30). The extent of some of this work can be realized from the fact that the New Jersey Station maintains 276 varieties of peaches and nectarines (a smooth-skin peach) on its breeding grounds for study and hybridization.
Objectives, of course, are different at different stations, depending on regional requirements and on the use for which the crop is intended. In general, there is still a need for a variety of high quality adapted to cold climates, and one that will not delay coming into leaf in climates where the winters are warm. Better varieties than Elberta—the best commercial peach so far—have been produced, but they are not so widely adapted. Promising hybridization work is now in progress with the Crawford type, which has very high quality, and with the J. H. Hale. A good deal of interesting genetic work has been done with the peach, but there is need for more.
Of the many species of plums native to various parts of the world, four are especially important commercially in the United States—the European plums, brought over by the first colonists, large, attractive, green and golden yellow (Reine Claude) to red and dark purple (Italian prune); the damsons of the Old World, yellow (Mirabelle) to blue (Shropshire), small, tart, used for preserves; the Japanese plums, introduced into this country in 1870, yellow overlaid with red (Kelsey, Burbank), excellent flavor; the native American plums, especially the Prunus Americana species (De Soto, Weaver), red to reddish orange, good quality but a thick, tough skin and clinging pit. These species are rich in varieties available as breeding material, and there are also many other interesting species.Several private breeders have done notable work with plums, including H. A. Terry and C. G. Patten, of Iowa, and J. W. Kerr of Maryland, who were interested in the selection of native varieties; Luther Burbank, who selected and hybridized Japanese plums and other species; Millard W. Sharp and A. F. and August Etter, of California, who are now engaged in hybridizing.
Much systematic hybridizing, both among the plum species and between plums and other stone fruits (cherry, apricot) is being conducted by State stations in California, Iowa, Minnesota, New York, and South Dakota, and by Federal field stations in California and North Dakota. Where the work has been longest in progress, as in South Dakota, New York, and Minnesota, several varieties have been introduced; elsewhere, promising material is still under test. The growing of plums has been declining in the United States during the first 20 years, and there is a great need for the breeding of varieties of really high quality adapted to regions characterized by extremes of heat or cold.
There are two species of cultivated cherries, the sweet and the sour. Sweet cherries are subdivided into two groups—heart or gean cherries, soft, tender, either dark colored (Black Tartarian) or light (Coe); and bigarreaus, firm, crisp, either black (Bing) or light (Napoleon). There are three groups of sour cherries—the amarelles, light (Montmorency); the morellos, dark (English Morello); and the marascas, native to Jugoslavia, used for making maraschino cherries. Duke cherries (May Duke) are probably hybrids between sweet and sour species. Other species useful in breeding include the Nanking cherry of Asia; the sand cherry, the western sand cherry, and the chokecherry of the United States; and the mahaleb cherry of Europe and the pin cherry of North America, used as rootstocks.
Commercial production of sweet cherries is practically limited to the Pacific and intermountain States, and that of sour cherries to regions along the Great Lakes. The trees are too tender for colder regions; they do not thrive in hot, dry regions; and in hot, humid regions cherry diseases are disastrous. Breeding work is very much concerned with overcoming these major handicaps and making this luscious fruit available over a much greater area, and also over a longer season.
There has been little work by private breeders, though the development of black bigarreau varieties (Republican, Lambert, Bing) by the Lewelling brothers founded the cherry industry in the Pacific States. Among State stations, New York (Geneva) has taken the lead, introducing two new varieties so far. South Dakota has introduced several varieties, and work is in progress at the Iowa and North Dakota stations, the Federal field station at Mandan, N. Dak., and in Canada, where one new variety has been introduced. In addition, collections of breeding material are maintained in Ohio, Colorado, Utah, California, and Oregon. In the search for necessary characteristics, native American mals cherries are being extensively used in some of this breeding work.
Apricots (probably native to China) are grown commercially only in Pacific Coast States because the blossoming habit of the trees makes them particularly susceptible to spring frosts in the colder regions. The species grown commercially is the common apricot, but several other species and subspecies are useful for breeding, including the black apricot, the Japanese apricot, the Russian apricot, and the Manchurian apricot. The raw material used by breeders consists largely of older varieties from England (Blenheim, Moorpark), from France (Peach, Guillans Early), and from the Union of Soviet Socialist Republics (Alexander, Budd), and newer American strains (Newcastle, Alameda). The chief objectives of breeders are to combine the good characteristics of these varieties and eliminate the faults; and also to develop hardier types adapted to a wider territory. Apricots from northern Asia are particularly hardy, but there is need for still more material of this sort.
Among the wide crosses that have been made is that of the apricot with the plum, producing the so-called plumcot—though some cytologists do not consider this a true hybrid.
Systematic breeding with apricots is quite new. The Department began work at Palo Alto, Calif., in 1922, and about 60 promising hybrids are now being studied and tested. Work began in New York (Geneva) also in 1922, and so far one variety (Geneva) has been named. In 1924 the North Dakota and the South Dakota stations began breeding work; the latter station has been experimenting with material from Manchuria and Siberia. Breeding work in Davis, Calif., began in 1930. Apricot-breeding projects are also in progress in Australia and Morocco.
Grown for thousands of years in the Orient, citrus fruits were established in Florida by 1579 and California by 1769 and were worth over 134 million dollars to growers in the United States in 1934. They are an outstanding source of vitamin C and an important source of vitamin B. Their unique sprightly flavors come from a combination of sugars (sweetness), acids (tartness), glucosides (bitterness), esters (aroma), peel oil (aroma). The chief types, including those used as rootstocks, are sweet orange, sour orange, King orange, tangerine orange, satsuma orange, shaddock, grapefruit, pummelo, citron, lemon, lime, Ichang (lemon), kalpi, calamondin, and kumquat.
Today, large production, decreasing returns, and increased competition place great stress on improvement by breeding. Breeding work was begun in Florida by the Department in 1892 and by the State stations in California in 1910, in Florida in 1924, in Alabama in 1933, and in Texas in 1934. It is being carried on in Hawaii, Mexico, Brazil, Argentina, Spain, Italy, Greece, Morocco, Palestine, Japan, China, India, Zanzibar, Australia, and New Zealand.
Improvement of citrus fruits in the United States prior to the use of modern breeding methods was by introduction of varieties from abroad, the selection of chance seedlings, and probably selection of some bud mutations. The record of the earlier development of varieties is full of interesting vicissitudes. Among the outstanding successes is the story of the Washington Navel orange. Through the help of a missionary, William Saunders, who was then Superintendent of Gardens and Grounds in Washington, D. C., got 12 navel orange trees from Bahia, Brazil, in 1870. Mrs. Eliza Tibbetts, migrating to Riverside, Calif., in 1873, took two of them along. They proved to be almost as important in California history as the discovery of gold, since all of California’s Washington Navel orange plantings came from these two original trees.
The objectives of breeders today include: Tree characters—compactness, vigor, productiveness, disease resistance, cold resistance, congeniality with rootstocks, and correct market maturity. Fruit characters—high dessert quality, seedlessness or near seedlessness, correct size and shape, good shipping and storage quality, attractive exterior, standard vitamin C content, firm pulp for canning, and attractive juice color. There are other special requirements for rootstocks. In the past the chief methods of improvement were by:
(1) Selection of superior seedlings without controlled pollination. Citrus fruits have the peculiarity of producing several seedlings from one seed. Usually only one is the product of the union of male and female parental cells; the others are practically buds within the seed tissue and are produced nonsexually. This adds to the difficulty of breeding work. (2) Selection of superior bud mutations. This has been very important since the intensive studies made by A. D. Shamel, of the Department, and his coworkers. In the last 18 years, probably 10 million buds have been sold to California growers alone as a result of this work. (3) Hybridization, especially between different species of citrus. This method is being used chiefly to create new types with unique flavors and other characteristics.
The last two improvement methods are still actively employed. Hybridization is being carried on by the Department and State stations, with promising results in several cases. Almost every kind of citrus fruit has been crossed with almost every other kind. Among the new types produced are the tangelo (mandarin orange X grapefruit); tangelo X grapefruit; tangerine X sweet orange; Perrine lemon (lemon X lime); citrange (trifoliate orange X sweet orange); citrangequat (citrange X kumquat); citrangedin (citrange X Calamondin); limequat (lime X kumquat); tangemon (mandarin X lemon); tangor (orange X mandarin); orangelo (grapefruit X orange); oramon (lemon X orange); lemelo (grapefruit X lemon); lemon X grapefruit; lemon X citron. The hybrids are so numerous and varied that naming them is becoming a problem in itself.
In connection with breeding work, several technical problems are being studied, especially polyembryony (the asexual production of embryos) and the inheritance of disease resistance.
While many of the subtropical fruits important in other regions, such as the loquat, juinbe, cherimoya, granadilla, jaboticaba, and white sapota, are relatively unimportant in the dietary and agriculture of the continental United States, others, such as the pineapple, fig, olive, avocado, and date, are the basis of established industries; and still a third group, including the mango, papaya, lychee, and guava, give promise of taking rank with those already firmly established. Most of those in the first group are adapted to one section or another of the United States, or to Hawaii, the Philippines, Puerto Rico, and the Canal Zone. With practically all of these fruits, breeding work and genetic studies are only at their beginning in this country, though there are some extensive and valuable collections of germ plasm made by such farsighted plant explorers as David Fairchild and Wilson Popenoe and their coworkers. Though the areas of possible cultivation are limited, interest in several of the subtropical fruits is growing, and with it the need for superior forms achieved through breeding. The raw material is fascinating in range and variety, and breeders are sufficiently well acquainted with it to have worked out techniques and determined the desirable objectives in considerable detail.
Fig growing is now the basis of a sizeable industry in California and Texas. Smyrna fig culture in California did not get into its stride until the discovery, at the end of the last century, that a small wasp, which makes its home in the inedible caprifig, is necessary for the pollination of quite a different type, the Smyrna fig of commerce. Improvement of figs—as of most other subtropical fruits—since that time has been largely by introductions from abroad and the selection of superior strains. However, hybridization has been conducted in California since 1922, and of some 4,000 hybrid seedlings that have fruited, several have been found with desirable characteristics. In Texas, hybridizing was started in 1935.
Avocado breeding is in the fortunate position of having a rich collection of varieties brought in by Wilson Popenoe and some of the early pioneers, available for hybridizing to obtain combinations of resistance to low temperatures, high quality, long range in marketing season, and other superior characteristics. These varieties are being intensively studied and several worth-while selections have been made. Although hybridizing has only begun, some excellent hybrids have already been secured and the future looks promising.
Thousands of date offshoots have been brought into the United States by the Department of Agriculture and others, totalling over 140 varieties, and of these some 16 varieties are now important in Arizona and California and many varieties are under test in Texas. Date breeding is an extremely slow process. Methods of controlled pollination have now been worked out, but progress so far has been by mass selection.
Pineapple growing has been revived in Florida since 1933; it is extensive in Hawaii, and fairly extensive in Cuba and. Puerto Rico. Hybridization has been begun by the Department; some work is being done in the Philippines; but most of the breeding work is in Hawaii, where promising results are being secured.
The papaya, a “tree melon", is counted an outstandingly fine fruit by those familiar with the best varieties. Florida seems best adapted to papaya culture in the United States, though the fruit is grown in California and Texas also. It is very important in the dietary in Hawaii, the Canal Zone, and the Philippines. The Department has introduced many strains and related species, and a breeding project is now in progress. Breeding work is also being done in Hawaii, the Philippines, and the Union of South Africa.
The mango, one of the oldest of cultivated fruits, with a flavor somewhat like pineapple and apricot combined, is grown in Florida— here over 200 introductions have been made by the Department, including more than 50 varieties and a number of related species—as well as in the island possessions of the United States. No method of controlled pollination has been worked out, but selection of superior seedlings holds considerable promise, and it is now being practiced in breeding for disease resistance and other characteristics.
Miscellaneous subtropical fruits with which little breeding work has as yet been done in this country include the olive, persimmon, granadilla, guava, feijoa, jaboticaba, pomegranate, jujube, lychee, loquat, white sapote, and cherimoya. All have possibilities for improvement and some are exceptionally interesting.
Until recent years there was practically no attempt to develop better nut trees by controlled breeding. Nature’s products usually seemed quite good enough. There is not much breeding work under controlled conditions today, but it has been started, and though the work has many difficulties, it also has very great possibilities for those with the inclination, the time, and the facilities to carry it on.
Chestnut breeding became a pressing need because the American Chestnut, a magnificent tree characteristic of large forest areas in the eastern United States, was practically killed out by chestnut blight, a disease from the Orient that first appeared on Long Island, N. Y., in 1904. Some hybridization of American and European chestnuts had been done before the blight appeared, but the hybrids were doomed because both parental species are highly susceptible. The Japanese chestnut tree is quite resistant, but the nuts lack flavor. Much more promising is the Chinese chestnut (first extensively introduced into the United States in 1907), which is highly resistant to blight and produces a nut as large as the European and often as fine in quality as the American. Present selection and hybridization work, therefore, is practically confined to the Chinese chestnut, with consideration being given to the Japanese. The Department and the Illinois station are engaged in this work, as are several private breeders. No varieties have been officially released by public institutions as yet. Chestnut blight will quite probably be overcome by breeding and it is not impossible that another major enemy, the chestnut weevil, will also be overcome.
Commercial filbert growing is confined to a region in the Pacific Northwest, particularly the Willamette Valley of Oregon and parts of western Washington naturally adapted to the superior filbert varieties of two European species (Barcelona, Du Chilly, Daviana, White Aveline are well known horticultural varieties of these). In the eastern United States these European filberts are handicapped by a fatal blight, which spreads to them from the American species, and by lack of winter hardiness. A few somewhat superior American varieties (Rush, Littlepage, Winkler) are available for growing in the East, but the breeding problem here is one of developing hybrids with resistance to disease and cold. In the Pacific Northwest, the problem is to develop filberts commercially and culturally superior to those now grown. There isa good supply of breeding material, and work is being actively carried on by the Department (at Beltsville, Md., and Corvallis, Oreg.), the Minnesota station, and the New York station at Geneva, as well as by several private breeders.
The breeding of pecans, the most important nut of the hickory group, is somewhat confused by existing uncertainties as to the sizes of nuts wanted by the market. The shelled-nut market wants very small pecans, and there is doubt as to whether they can be grown profitably except in uncultivated forest groves. The one-time demand for very large pecans has steadily diminished, so that breeding for extra size no longer seems desirable. In addition, most of the best of the older varieties of pecans proved to have so many drawbacks that the nuts are no longer marketed by varieties (as are apples and pears), but the varieties are blended. Nevertheless, selection and hybridization proceeds with certain definite objectives—hardiness (for northern pecans), disease resistance, fruitfulness, size of nut (at present a compromise), shell thinness, shelling quality, kernel quality. The work of the Department is divided regionally; the Illinois Station is carrying on a selection project; several private breeders are active; and pecan breeding by selection is being conducted in New South Wales and in Mexico.
Hickories other than pecans have received very little attention from breeders—the market demand is too limited. Nature has accomplished considerable hybridization between the various species (pecan, shagbark, shellbark, bitternut), and trees of some hybrid forms are available commercially. Hickories superior in thinness of shell, cracking quality, and flavor would fill a real need. A limited amount of selection work is being done by the Department of Agriculture, the stations in Illinois, Ohio, and New York (Geneva), and private breeders.
Breeding the Persian walnut (called English walnut because it first came to this country from England) has largely been confined to selection, which has about reached its limit of practicability. The next step is hybridization to develop varieties resistant to blight and possessing greater fruitfulness, superior hardiness, better cracking quality, and superior flavor. Such work is being conducted by the Department, the Minnesota and New York (Geneva) stations, and at least one private breeder. Selective breeding is being done in Mexico.
Selective breeding with the eastern black walnut is being conducted by the Department, the Illinois, the Minnesota, the Ohio, and the New York stations, and many private breeders. Similar work with the Japanese walnut (much like the butternut) is being conducted by the Connecticut station and several private breeders. The Department is now starting a project to create a form of walnut unlike any now existing by crossing the Persian walnut with the butternut for hardiness and flavor, then with the eastern black walnut and the Japanese walnut for sturdiness and fruitfulness of tree.
Almond breeding is being systematically carried on by the Department in cooperation with the California station at Davis, with the objective of combining in a few new and definitely superior varieties as many as possible of the superior characteristics of the existing varieties. If this is successfully done, American almonds should not only dominate the American market but have a place in foreign trade. Practically no breeding work has been done with the pistache nut (adapted to hot, dry regions), though it deserves attention. The tung tree, the nuts of which furnish a valuable oil that dries more rapidly and is more resistant to water than linseed oil, was introduced into this country from China by the Department of Agriculture in 1905. The Florida Station began hybridization work in 1929, and the Georgia Station began selective breeding in 1933.
Very little genetic analysis has been made with nut trees, but a good deal of valuable technical work has been done on pollination technique, pollen viability, receptivity of the stigma, fertilization, and incompatibility.
The enormous number of our named varieties of flowers has resulted from generations of breeding effort on the part not only of commercial growers but of untold numbers of amateurs from every walk of life. There are 15,000 varieties of roses alone, 8,000 varieties of tulips, 7,000 varieties of dahlias, 7,000 varieties of narcissus. Many of these are romantic in origin and testify to the deep love of the breeder for his work.
Yet most of this work has been unscientific in nature, and too much of it still is. Flower breeders, both amateur and professional, have on the whole had only a slight acquaintance with the modern science of genetics, which has played so important a part in the breeding of the more important food crop plants. They proceed by trial-and-error methods and wait for the breaks, and the result is much waste of time and effort, and the persistence of practices that cannot bring the expected results. Modern genetics goes out and makes the breaks. The time has come when those interested in breeding flowers should go to some trouble to study the facts and theories of heredity developed since Mendel’s paper was rediscovered in 1900, and to master the technical methods that have revolutionized other fields of plant breeding. Genetics has a vast amount to contribute to the improvement of flowers, though professional geneticists have paid relatively little attention to ornamental plants except as these have been used as laboratory material for the study of theory.
Flowers differ in their requirements for pollination, depending on structure of the flower parts and on different degrees of self- and cross-sterility. Emasculation (removal of the anthers) is quite commonly necessary in cross-pollination, and the bagging technique must frequently be used to prevent contamination with unwanted pollen. The older method of improvement was by selecting superior plants from a large mixed mass; it is still widely used, but it is slow and very limited compared with later methods. Then came line breeding, or selection from the progeny of a single plant. Hybridization, the most important method in plant breeding today, will probably be used more and more with flowers; but what some flower breeders fail to realize is the necessity for continuing the breeding work after the first hybrid generation, to provide segregating groups with different combinations of parental characteristics; and also the necessity for keeping the right kind of records. Unusual plants produced by gene mutations or by variations in the number, structure, or behavior of chromosomes are sources of valuable material, and some of the newer methods of artificially bringing about these changes seem promising for the flower breeder. This emphasizes the need for an understanding of chromosomes, which has contributed definite practical results—notably, for example, in the case of double-flowered stocks—and will contribute much more.
Representative flowers considered are the amaryllis, China-aster, canna, carnation, chrysanthemum, dahlia, gladiolus, hemerocallis, iris, lily, nasturtium, rose, snapdragon, double-flowered stock, and sweet pea. Some of these have a rich historical background and several have been subjects for much patient selection and hybridization. In two cases—the China-aster and the snapdragon—breeding has been responsible for the development of forms resistant to destructive diseases. In all cases there are as yet untouched opportunities for improvement through better breeding methods, a closer study of inheritance and cytology, or the use of germ plasm not yet incorporated into our cultivated varieties.
Among the Cinderellas of the plant world are many humble legumes—relatives of our common peas, beans, alfalfa, and clover—that are valuable for soil building and conservation because they will thrive where better-known crops fail, and they enrich the soil with nitrogen. Some are known as weeds; some have been grown by farmers here and in other countries both for forage and for human food. Not much has been done to study the adaptability of these plants to special conditions or to explore the possibility of improving them by breeding; but as this country passes out of the large spending stage in agriculture, they will be given more attention. Their use is like having a savings account in the bank.
A few of these plants are already of considerable value. The cowpea is extensively grown, a large number of varieties are recognized, and some State stations as well as the Department have carried on breeding work with it. At least one outstanding variety, the Victor—resistant to wilt and nematodes—has been developed by controlled hybridization, and others have resulted from selection. The field pea, also widely used, has given good results with selection and is now the subject of breeding programs by the Department and by the Georgia, the Alabama, and the Tennessee stations. The velvetbean is a leading legume crop in the Southeast; several superior varieties have resulted from selection over a period of years, and a breeding program with this crop would probably be profitable. A large number of species of vetch are in general use, and the Oregon station, cooperating with the Department, has led in developing improved varieties. The lespedezas or bush clovers, invaluable in southern. agriculture, have recently been receiving considerable attention.. New varieties have been introduced from Japan and Manchuria, and the Department has been carrying on active selection work, but the possibilities are by no means exhausted as yet. The bur-clovers are grown to some extent and have received some attention from breeders, but the species has rich possibilities not yet explored. Rattlebox (crotalaria) is a new forage plant in the United States, and the Department, cooperating with the North Carolina, South Carolina, Georgia, and Florida stations, has been selecting early varieties. Kudzu and the peanut are grown as forage crops, but no breeding work has been done with them from this standpoint.
Among the completely or almost completely neglected legumes, some of which undoubtedly have potential value in the United States, are the milk vetches for arid conditions; beggarweed or tick trefoil; bonavist, long grown in Africa and Asia; the chickpea; fenugreek, grown to some extent in California; the grass pea and guar, both used in India for animal and human food; kidneyvetch, the subject of breeding programs in Wales and Denmark; Lotus, commercially important in Europe and Australia; lupine, now being bred by German and Russian workers; the pigeonpea, a valuable legume in tropical countries; sainfoin, long grown in Europe; serradella, used in Europe on acid sandy soils; Sesbania, adapted to wet soils in the South; sulla, used in Europe and Australia.
Interesting technical studies with some of these plants, both in the United States and abroad, have helped to develop fundamental facts useful in breeding.
Man lives largely on grass. His grains are grasses. His meat and milk are transformed grass; in the United States, grazing lands furnish nearly half the sustenance of livestock. In addition, grasses are of great importance in reducing erosion and maintaining soil fertility; and is country spends over $100,000,000 a year on private lawns, and some $90,000,000 on turf for other purposes. Systematic efforts to improve grasses by breeding are therefore of major importance. In the United States these efforts with the miscellaneous grasses are relatively new; many State projects were begun not more than 5 years ago―though sporadic work has been going on for a long time—and it is too early to expect results. The work is older in Canada, the British Isles, New Zealand, Australia, Sweden, Germany, Denmark; and probably more has been accomplished at Aberystwyth, Wales, than anywhere else. But modern genetics proves that plants must be bred for specific environments. We shall have to solve our own grass-breeding problems.
The sources of breeding material are as wide as the world, for each region, from desert to swamp, from the Arctic to the Equator, from mountain to sea beach, has its peculiar grasses, adapted to persist and thrive there. The number of grasses developed under these varied conditions is extremely large and the range in characteristics correspondingly great. Long ago the migration of grasses to other regions began. South American cattle live on forage grasses that originated in tropical Africa, cattle in the Corn Belt on grasses from Europe. The United States today may be divided into six regions from the standpoint of climate, and the major types of grasses in these regions into nine broad groups—Kentucky bluegrass, Canada bluegrass, and timothy; the redtop and bentgrasses; orchard grass and tall oatgrass; Bermuda, Johnson, and Dallis grasses; carpet, Napier, Bahia, and Para grasses; awnless bromegrass and crested wheatgrass; native short grasses and prairie grasses; slender and western wheatgrasses; Sudan, reed canary, and other grasses.
What are the needs and possibilities for improvement by breeding? Shy seed production handicaps the use of many valuable grasses. Diseases play havoc in certain regions and with certain types. Some excellent grasses are not aggressive enough in growth to maintain themselves in competition with other ae others are too aggressive to make possible the maintenance of desirable legumes in mixture. Some are not vigorous enough in renewing growth after grazing or cutting. For some pasture and range uses increased longevity is needed, and this may be largely affected by drought resistance and winter hardiness. Greater ability to thrive in wet and in saline soils is very important in some places. Some good grasses would be more useful if they were more palatable to livestock and had higher nutritive value. In turf grasses, texture, ability to withstand hard usage, and uniformity are of major importance. On all of these eight counts there are sufficient variations within the best-adapted types to give promise that breeding by selection or hybridization would accomplish improvements. Already, selective breeding work in the United States has furnished improved new strains, either introduced or soon to be ready for introduction, of Washington and Metropolitan bent, velvet bent, highland reed canary grass, tall fescue, tall oatgrass, Bahia grass, tift Bermuda grass; and in Canada, of slender wheatgrass, crested wheatgrass, bromegrass, and orchard grass. Twenty- three additional improved strains in Canada are being increased for more extended trials and distribution.
The manipulations in grass pollination by controlled methods are often as fine as jeweler’s work and must be performed under a magnifier or microscope. Ingenious techniques have been developed, and much study has been given to flowering habits, to the question of self sterility, and to chromosome behavior, especially in wide crosses. There has been little work as yet on the mode of inheritance of characteristics.
Timothy, the most important of the agricultural grasses, was first cultivated in North America, though it is of European origin. It received its present name, Metab from Timothy Hansen, who introduced it into Maryland from New England or New York about 1720. In 1929, one-third of the total acreage in hay in the United States was all or part timothy. It is also widely used in pastures, being one of the most palatable pasture grasses to livestock.
Varieties and strains of timothy differ rather widely in earliness or lateness of maturity, length and degree of fineness of stems, width of leaves, tendency for the leaves to remain green, resistance to the principal timothy disease (rust), and in other ways. These variations are the basis for breeding improved kinds. The objectives of breeding programs include rust resistance, increased productivity, early varieties for the South, late varieties for the North, varieties adapted for hay production when grown in mixtures with clover or alfalfa, and varieties especially suitable for use in pastures.
Timothy is normally cross-pollinated, so that most of it is quite hybrid in make-up. Methods of breeding include repeated selection among open-pollinated strains, and also some self-pollination and crossing of inbred lines.
Up to the end of the last century, timothy was timothy; there were no improved varieties, as there were of wheat, oats, and other grains. In 1889, Willet M. Hays pioneered in making selections of timothy plants at the University of Minnesota, for increased productivity and a longer harvesting season. In 1894, A. T. Hopkins, a well-known entomologist, began making selections and continued the work for several years. Hopkins had a notable faculty for arousing enthusiasm in others over the possibilities in timothy improvement.
After 1900, timothy breeding was started at Cornell University and is still being carried on there. An early and a late variety, both somewhat rust-resistant, have been produced, and a number of technical studies have been completed. Other stations that have had timothy breeding programs include those in Iowa, Minnesota, Pennsylvania, Kentucky, New Jersey, and Wisconsin. Some breeding work was conducted by the Department from 1899 to 1909, and thereafter it was carried on more intensively in cooperation with the Ohio Station. The outstanding variety developed from this work is the Huron—late, leafy, rust-resistant—released in 1933.
Abroad, several varieties with regional adaptation have been developed at Svalöf, Sweden, and at the Welsh Plant Breeding Institute, Aberystwyth, Wales. Notable among Welsh developments were low-growing types that root at the nodes, especially suitable for pasture. These have been tried only to a very limited extent in the United States. Timothy-breeding work has also been carried on in other European countries.
Technical studies with timothy include biometrical analyses of field trials, determinations of chromosome numbers, seed production under self-pollination, self-sterility, and effects of selfing on vigor, yield, disease resistance, and other characteristics.
Alfalfa, which means “best fodder” in Arabic, is very old. One writer has suggested that it was the “grass” on which Nebuchadnezzar fed when he was driven into the fields. It was fed to sleek chariot horses in ancient Rome. The Spanish conquerors of Mexico and took the Indians’ gold but brought them alfalfa seed. Forty-niners, sailing to California around the Horn, picked up some Chilean alfalfa and took it with them. It soon spread to other Western States.
It did not winter well in the North. But in 1857 Wendelin Grimm, German immigrant, brought alfalfa from his homeland into Minnesota. For 50 years he stubbornly and patiently saved seed from plants that survived the winter. In the end, he had the one hardy alfalfa. Subsequently, experiment station workers made Grimm alfalfa famous.
This was both a boon and a drawback. Grimm alfalfa was so satisfactory that there was little incentive to develop other improved varieties. Nevertheless, between 1903 and 1915 a number of State and Federal workers were busy breeding alfalfa, and they did some interesting work introducing varieties that are now standard— though the limitations of the methods they used were not then fully understood. This work was stopped by the World War, with its emphasis on food crops rather than feed crops.
Some years later, stands of Grimm and other alfalfas began to die out prematurely and alarmingly, first in Iowa, Kansas, and Nebraska, then in other Midwestern States. By 1925, Federal workers traced the mysterious destruction to the organism now known as the insidious phytomonas—Phytomonas insidiosa. Today it costs farmers several million dollars a year in lost alfalfa crops and expense of reseeding. This catastrophe put pressure on breeders to see what they could do.
Plant explorers of the Department have scoured the earth for alfalfas, bringing back a thousand different strains. None proved to be very resistant to the disease except some from Russian Turkistan, northern India, western China, northeastern Iran. The chief problem in the present breeding program, then, is to combine the resistance of these strains with the good commercial qualities found in Grimm and other American alfalfas. Dovetailing with this is another problem of developing strains especially well adapted to various broad regions in the United States. Other desirable objectives include heavier seeding, better forage quality, suitability for grazing, insect resistance, drought resistance, and higher protein content.
For a concerted attack on these problems, State and Federal breeders have recently organized the Alfalfa Improvement Conference, to insure close cooperation between all the workers concerned.
Work has been done on breeding technique; correlations between various characteristics in alfalfa; hybrid vigor; inbreeding and its effects; the possibility of making species crosses; and segregating and purifying strains for disease resistance and cold resistance, with the object of recombining them. The general genetic behavior of alfalfa has been explored, but little has been done on the inheritance of specific characters. Recently a number of workers have been interested in the cytological study of the plant.
In the Orient soybeans have been grown since time immemorial, and it has been said that some oriental countries could not exist without them. The plant was introduced into the United States (Pennsylvania) as early as 1804. Since 1890 most of the State stations have experimented with it, but it aroused comparatively little enthusiasm until the last few years. In that time its rise has been dramatic. Acreage has increased 110 times in 28 years, seed production 13 times in 15 years. The United States is now second in seed production to Manchuria, though still far behind that “Land of Beans."
The reason for this phenomenon is to be found in the versatility of the soybean. Every part of the plant is useful, and a tabulated list of uses takes up a page of fine print. Forty-five oil mills in the United States are now crushing soybeans; 40 concerns are manufacturing soybean food products; 75 factories are turning out industrial products made from soybeans.
Altogether, the Department of Agriculture and State stations have brought in some 10,000 selections for testing and experiment. Thirty-two stations and the Department are engaged in breeding work. About 100 varieties have been introduced for commercial growing since 1894. Yet the breeding work is only at its beginning, for several reasons.
The soybean is very particular in its local requirements. This means that special varieties for each kind of use have to be developed for each separate region or locality. This has long been done in the Orient. The uses themselves demand quite distinct characteristics. Thus beans grown for oil should have a high oil content and a high iodine number, which is associated with good drying quality. The lecithin content of the oil is also important for some industrial uses. Beans for certain industrial uses should have a high protein content. Beans grown for food protein should be high in the three amino acids, cystine, tryptophane, and tyrosine. Those grown to be cooked as dried whole beans should be tender and of excellent flavor. Those grown for use as green shelled beans must be especially adapted to this purpose. And so on.
Progress has been made in developing varieties for local use that meet these needs. But there is much still to be done. The breeder, however, has a wealth of material,and the measurements and tests already made indicate the range of some of the characteristics among different varieties. Oil content, for example, ranges from 12 to 26 percent, iodine number from 118 to 141, protein content from 28 to 56, lecithin content of the oil from 1% to 3 percent; the percentage pf the amino acids mentioned varies over a wide range. The breeder can choose and combine, build up this, reduce that. Diseases are not yet serious factor with soybeans in this country, but it is known that resistance to several diseases varies also, and when that complication enters he has some information on which to proceed.
The soybean is a self-fertilized plant, and artificial crossing is difficult and tedious. Hybridization, however, offers the best means of combining desirable characteristics and getting a wide variety of segregates from which to make selections. The inheritance of a good many characteristics of the flower, stem, leaf, and seed has been worked out, and a beginning at least has been made in mapping the location of a few genes on the chromosomes.
The ancient belief that clover brings luck has proved to be abundantly true for agriculture. First grown as a cultivated crop in the 16th century, its use became the foundation for good farming practice. It is at once food for the land and food for animals. Systematic improvement by breeding, a recent development, is being carried on in several countries.
Natural adaptation has been the prime factor in developing regional strains of red clover—the most important of the clovers in the United States that differ in productivity, winter hardiness, and disease resistance. For several years, these regional strains have been closely studied by the Department in cooperation with the Kentucky, Ohio, and Iowa stations, partly to determine regional needs, partly to discover superior plants that may be used in breeding. Broadly, the chief objectives for the three red-clover regions of the humid eastern United States are: Southern—disease resistance, especially to anthracnose; central—disease resistance and winter hardiness; northern— ability to withstand a long period of winter dormancy. In addition, powdery mildew, the potato leafhopper, and the clover root borer are clover enemies in all regions.
So far, anthracnose-resistant strains have been developed by the Tennessee and Kentucky stations, and the Department of Agriculture has during recent years cooperated in improvement of the strains developed by the Tennessee station many years ago. Lines resistant to powdery mildew have been developed in cooperation with the station in Wisconsin. Other developments are in progress in cooperation with the Illinois Station; and the stations in Minnesota, Pennsylvania, Tennessee, Indiana, New Jersey, and Idaho have red clover breeding programs under way. Abroad, nearly all European countries, and Australia and New Zealand, are doing breeding work with red clover, and in several of these countries superior strains have been introduced. Selection from natural stocks has played a large part in improvement programs, but the isolation of self-fertile lines and controlled crossing are also used. The Welsh Plant Breeding station has carried on important basic studies.
There has been no breeding work with white clover in the United States, but work has been done in New Zealand, Denmark, Sweden, Finland, and Wales. Crimson, alsike, subterranean, berseem, and Persian clovers have not been bred in this country, though some of them have received attention abroad.
Sweetclover, which was classed as a weed a few years ago, has had a phenomenal rise in popularity and now holds an honorable place in the agriculture of the north-central region and the Great Plains States, as well as in several foreign countries. Several varieties, resulting from selection and introduction from abroad, have been introduced by the Department of Agriculture, by several State stations, and by individuals. Canada leads in systematic breeding, and work is also in progress in Wisconsin, Minnesota, Kansas, Washington, Texas, Nebraska, Illinois, West Virginia, and Idaho, as well as in the Union of Soviet Socialist Republics and in Germany. One of the chief objects in all breeding studies is the development of strains low in coumarin, since the presence of coumarin or of closely related substances appears to make spoiled sweetclover hay toxic to livestock and lowers the palatability of the green plant. So far, the results in this direction are promising.
Studies have been made of fertility and sterility relationships in clover that have cleared up misconceptions, and pollination techniques have been developed. There have been some cytological investigations and genetic analyses, especially in sweetclover.
Beer is made with hops, water, malted barley and other cereals. The hops supply lupulin (resins and essential oils) which gives the beer its characteristic flavor, and tannins which help to clear it. Thus hop growing is vital to the brewing industry, though unfortunately for growers, a small quantity of hops makes a great deal of beer. In Europe hop growing goes back at least to 768 A.D. Kings who liked hopped beer sometimes compelled farmers to grow hops by law; those who preferred beer without hops forbade farmers to grow them. Kings of the latter type were apparently in the minority, and in Europe much effort was devoted to improving hop varieties.
The hop is a peculiar species. It is a perennial vine, grown on poles or trellises, and extremely sensitive to sun, wind, heat, rain, insects, and diseases. Male and female flowers are borne on separate plants, though it is not unknown for a plant to change its sex, sometimes more than once. The hop of commerce is something like a fir cone but more papery and fragile, and it is borne only on the female plant. Fertilization is not necessary for the development of the hop, but the cone bears seeds only when the flowers are fertilized.
Commercially hop vines are reproduced by cuttings, like sugarcane and some other plants. Since the seed is always a product of cross- fertilization, the plants are of hybrid origin genetically, and seeds from the same mother will produce many different types. It is chiefly from these diverse seedlings that hop breeders get their raw material for superior selections. Hop breeding presents some especially knotty problems and has some difficulties similar to those of animal breeding. Because the male plant bears no cones, it is uncertain just what it contributes to improvement, even when controlled pollination is practised so that the nature of the male parent is known.
Breeding work in the United States is relatively new. It was started by the Department of Agriculture in 1900, but later the World War discouraged and prohibition finished it. Now, however, it is being continued again in cooperation with the Oregon station. The chief objectives are increased yield; favorable periods of maturity; resistance to several diseases, especially downy mildew, the bane of growers in various sections; and quality, an elusive character depending on type, color, soundness, and lupulin content. Of these, only the amount and quality of lupulin can be accurately measured by laboratory methods. The importance of quality may be better understood from the fact that at present brewers in this country frequently mix some European hops with their American-grown hops and usually pay a high premium for hops from Germany and Bohemia.
Thus far the breeding program in the United States has been concerned largely with making a close study of the available raw material so that an accurate catalog of plant characteristics may be available. Ithas been necessary to work out techniques for some of the more difficult problems such as control of pollination, evaluation of breeding methods, controlled development of the downy mildew disease, measurement of resistance, and determination of quality. With these difficulties on the way to solution, a basis is being laid for future breeding work. Good results with seedling selection in Europe indicate the possibilities, though improved European varieties have failed to give comparably good results in this country. Growers on the Pacific coast are now very much interested in hop improvement by breeding, and the New York (Geneva) station has also recently initiated a varietal improvement project.
In forestry, genetics is almost a new word, and breeding as it is practiced with other economic plants is a virgin field, Economic pressure in the wood-using industries and the urgent national need to build up forest areas, however, have turned attention to tree breeding as a vital part of an intelligent forest program. There is ample evidence that, like other plants, forest trees differ individually in the characteristics that are of value to man; and the possibility of breeding superior individuals and populating large areas with their descendants, as is done with wheat and other crops, is one we cannot escape exploring.
Obviously there are difficulties not involved with small, quick-maturing plants, in many of which pollination is fairly easily controlled, and it will take a good deal of study and ingenuity to overcome some of these difficulties. The methods and possibilities, however, are fundamentally the same as with other plants. They include a clear formulation of the type of tree desired for a given use; the selection of superior individuals by extensive testing and observation; establishing pure lines where possible; as much use of vegetative propagation, by cuttings, etc., as possible, to reproduce superior individuals absolutely true to type; the crossing of strains, varieties, species, and genera, both to create new types and to obtain hybrid vigor; a thorough study of polyploids—that is, individuals with an increased number of chromosomes in the cells beyond the normal number—as sources of especially valuable stock. At present, polyploids are receiving special attention because these plants with extra chromosomes are so often characterized by unusual size and vigor, but the enlarged cell size in some types of polyploids, resulting in coarseness of structure, may prove to be a drawback for many commercial uses.
It need hardly be said that research in the cytology of forest trees, particularly in cytogenetics, and in the mode of inheritance of characteristics, should be carried on along with a practical program. Much work is also needed to determine standards and tests applicable in the forest and in the selection nursery.
In every one of these fields, a beginning at least has been made. Fairly extensive tests are being conducted to determine superior varieties and individuals for both regional forest requirements and use requirements, and these tests include disease resistance, weather resistance, rapidity of growth, and other important characteristics. Hybrids, superior in various ways to either parent, have been made, a notable example being the creation of fast-growing poplar hybrids for paper pulp. Experiments are being carried on in methods of control- led pollination and vegetative propagation. Efforts are being made to devise better progeny tests—not an easy matter under practical forest conditions—and ways to reduce the time involved in testing. Perhaps the least work is being done in fundamental research in genetics; but so far there are very few geneticists in forestry—practically none in comparison with other branches of agriculture.
To other plant breeders the amount of breeding work in forestry would seem small indeed, and doubtless quite elementary in nature. Nevertheless, the foundations necessary for a science of forest genetics are being laid, in the United States and in other countries. Moreover, the forest-tree breeder, challenged as he is by difficulties, is in the stage where he is filled with enthusiasm for the possibilities not only of eliminating some of the most costly mistakes of past forestry practice, but of adding something genuinely valuable to nature's own magnificent achievements in creating trees useful to man.
The goat performs two useful functions. It cleans up brush, thereby saving its owner a great deal of work; and through its digestive processes, it converts the brush into food and clothing for man, in the form of milk, meat, mohair, and skins.
The domestic goat is probably descended from the pasang or Greek ibex of the Near East. The long-haired Angora was originally developed by the Turks centuries ago. The first importations to Europe were apparently made in the sixteenth century, and to the United States as late as 1849. South Africa, Turkey, and the United States are the leading producers today. There are now over 3 million Angoras in this country, and the industry is concentrated chiefly in the Southwest, with Texas well in the lead. Of the 15 million pounds of mohair produced in the six leading States in 1935, Texas produced 13 million.
Improvement of the Angora goat has been entirely in the hands of private breeders. In the range herds, it has been carried on by the method of breeding high-grade does to registered bucks that conform to the standards of the breed association. Very little research work on breeding or genetics has been done by public institutions. The station near Sonora it is now carrying on three active projects on inheritance of type, inheritance of cryptorchidism or undescended testicles, and cytological and hybridization studies.
The best present representatives of the breed produce up to 75 percent more mohair than the average for the country. But there is a very great lack of uniformity even in good herds. If further progress is to be made, a research program will be needed to work out better methods than those now in use to determine an animal’s inheritance, and a far better knowledge of the mode of inheritance of characters concerned in the production of good fleeces. Research usually pays well, but there are many difficulties and complications involved in such a program, and it can only be carried on with the active encouragement of the industry.
Meanwhile certain practical steps might be taken by the industry that would tend in the right direction. Among these would be a system of pedigree recording based on production of mohair, with certification of the records, as with dairy cattle and poultry; the selling of mohair on a quality rather than a weight basis, to stimulate improvement of the breed from this standpoint; and the adoption of different methods of awarding prizes at shows, on the basis of get of sires and outstanding families rather than individual appearance—a practice that would be in line with the use of the progeny test, which is overwhelmingly important in evaluating breeding stock, whether plant or animal.
The milk goat is a handy pocket edition of the cow, and it will subsist where the keeping of cows is impracticable. In certain areas and under certain economic conditions, it can be an important factor in contributing to the family food supply. The milk is not significantly different from cows’ milk in nutritive value, and goat meat is palatable and wholesome. The official maximum production record in the United States, made by a Saanen doe, is nearly 7 quarts a day for a period of 9 months and 10 days. Average production is very much under this, and there is great variability between individuals.
Efforts to improve the productivity of milk goats in the United States, therefore, are worth while not only from the standpoint of the present industry, with its breeding and dairy investment, but also as one method of economically raising the nutritional level of some sections of the population.
In this country, only two projects have been carried on by public agencies involving research and experiment in milk goat breeding — one conducted by the Department, one by the New Mexico station.
The Federal project was started in 1909. It has consisted largely in grading up common American does by crossing and top-crossing with registered Saanen and Toggenburg bucks. Progress has been slow partly because of the very small number of breeding does used. However, the average length of the lactation period has been increased 145 percent over that of the native does, and the average annual milk yield by 335 percent. Analysis shows that the period of maximum production is between 4 and 6 years of age. Index measurements of the sires used show marked differences in ability to transmit superior inheritance to daughters.
At the New Mexico station, native does have been graded up by the use of registered Toggenburg bucks, and studies have been made of the inheritance of horns and wattles, length of gestation, prolificacy, sex ratio, and the effects of inbreeding and outcrossing on milk production and birth weight of kids. Marked increases in production were obtained from the top-cross does, and several does in the herd have made creditable records under advanced registry. Line breeding was practiced with three outstanding bucks, the results indicating that it would be worth while to continue this as an experimental procedure. Fertility in the herd was high, 144 parturitions producing 286 kids.
Other researches with milk goats include nutritional experiments with the milk and studies on the physiology of milk secretion, including the effect of pituitary extract on lactation. There has also been a limited amount of genetic research on inheritance of horns, wattles, short ears, color, cryptorchidism, multiple births, and a peculiar nervous instability.
Improvement of herds bas been mainly in the hands of private breeders and their three registry associations. Considerable progress has been made, but more might be done by the keeping of more complete records; the development of a more extensive record-of-performance program; the more extensive use of proved sires through a system of exchanges; the elimination of factional tendencies among groups of breeders; and the working out of better procedures for the selection of breeding animals. There is a need also for further research and experiment on the uses of goat products, and for more study of the economics of production.
Dogs supplement the brains of men. Their usefulness depends almost entirely on intelligence and temperament. No other animal serves so many purposes; they are hunters, guards, companions, guides, messengers, herders, detectives, haulers and carriers, scavengers and even, in parts of the world, sources of fur and food. It is surprising, then, that so little has been done in the way of systematic research in the genetics of the dog, in spite of the fact that in other fields—physiology, psychology, medicine—work with dogs has helped to make possible some major scientific advances of great benefit to humanity.
Scattered studies have furnished information on the inheritance of coat colors, which apparently depend on many genes, often with multiple effects. Certain characteristics of form and structure have also been studied, including the inheritance of modified secretion of the endocrine glands, which has been under investigation by Stockard the Cornell University Medical College. Some work has been done on the inheritance of aptitudes, notably at Fortunate Fields, in Switzerland, where German Shepherd dogs have been trained as guides for the blind for army and police service. Here marked progress has been made in breeding superior animals by assuming that valuable characteristics were controlled by a few major genes.
In practical breeding, dog competitions of various kinds have had a marked influence, since persistent winners at field trials and dog shows have a favored position as breeding stock. On the whole, this has probably been a good influence in dog breeding, though from the standpoint of sound scientific practice undue weight is given to the appearance or performance of the individual animal. Awarding prizes and selecting breeders on the basis of a genuine progeny test would put dog breeding on a sounder genetic foundation.
In some cases these contests have been responsible for splitting a breed in two different directions, one strain being especially adapted to perform well in the field, the other being notable for show points. The field competitions—greyhound racing, dog-sled racing, hunting and retrieving contests, sheep-herding contests, obedience trials—are of interest as indicating certain kinds of measurements that would have to be developed in a program of genetic research so that one dog might be accurately compared with another.
What are the possibilities in genetic research for the future? There is little doubt that it would help to accomplish improvements in dogs themselves, especially in the development of types for special purposes. Beyond this, however, is the fact that dogs are probably better suited than any other animal for investigations in the inheritance of psychological traits. These traits are important in many farm animals; nothing is known about their behavior in heredity. The Department of Agriculture has recently made a modest beginning in an investigation of this sort, using the Puli dog—a sheep dog of Hungary—which is being crossed with various other breeds. From these experiments it is hoped that worth-while information may be developed regarding the inheritance of intelligence and certain aptitudes of practical value in dogs, the influence of temperament in such problems as effective feed utilization, and the possibilities for similar investigations with other farm animals.
Before the nineties, this country produced turkeys at the rate of 1 a year for every 5 persons. In subsequent years the blackhead disease, scourge of turkey growers, reduced this to 1 for every 15 persons. Recently research taught us how more nearly to control blackhead, and the number of turkeys has now risen to 1 a year for every 6.5 persons. But less scientific attention has been paid to breeding problems than to those of feeding, management, and disease control.
Our modern domesticated turkeys are descended from the North American or common wild turkey, of which there are five subspecies. Wild turkeys were apparently domesticated by the American Indians, and some of them were taken to Spain as early as 1498. Several European domesticated varieties were developed from this ancestry, and some of these were brought back to the colonies to become the foundation stock of our six present American breeds—the Bronze, the Narragansett, the White Holland, the Beurbon Red, the Black, and the Slate. The differences between these breeds are largely in plumage color.
Several major objectives stand out as desirable in turkey breeding, though little in the way of coordinated or intensive work has been done toward achieving them. (1) There is an increasing demand for a smaller bird to meet the needs of the average family. Hitherto, breeding has tended toward increased size. There is still a demand for large birds for hotels, etc., but they now actually sell at a discount because of the greater demand for smaller sizes. This situation can be corrected by breeding (2) There is need for improved body type to provide a larger proportion of meat to bone, especially on legs and breast. (3) Birds should be bred to reach market maturity at an earlier age. (4) Higher egg production is desirable, especially in making possible an earlier and longer laying season, which now covers a maximum of about 6 months.’ (5) Higher fertility and hatchability of eggs are desirable to reduce production cost. (6) Attention should be given to breeding for lower mortality, whether from disease or other causes.
In achieving such ends, use might be made of a breeding system based on production records, pedigrees and, progeny tests, such as that now used by progressive breeders of chickens. There is need for more trap nesting and pedigree recording to serve as a basis for isolating superior families and breeding from them. State and Federal agencies might well Jead the way by developing strains notable for viability, quick maturity, and good market quality.
The small amount of genetic research with turkeys at State stations has been concerned with tracing the inheritance of plumage colors. The Department has experimented in making crosses between turkeys and chickens. All the hybrids died as embryos, though one lived almost to the hatching state. At its range experiment station in Montana, the Department carried on a 5-year inbreeding project which indicated the possibility of establishing inbred lines not inferior to outbred turkeys in fertility, hatchability, production, and weight of eggs. A similar outbreeding project was successful in improving fertility, hatchability, and production of eggs, and maintaining egg weight.
There are places along the South Shore of Long Island, N. Y., where for many miles the air is filled with the quacking of ducks, and the creeks and small coves are white with the birds. This is the center of the commercial duck industry. The flocks are all Pekins, which are sold as “green ducks” at the age of 9 to 13 weeks, after a period of rapid fattening. Elsewhere in the country there are a few commercial duck farms, and ducks are raised as a side line on farms in every State. The Pekin is everywhere the outstanding breed, though the Rouen, Aylesbury, Cayuga, and Muscovy are also represented among the meat breeds; the Indian Runner among the egg breeds; and the White Call, Grey Call, Black East India, Mandarin, and wood duck among the ornamental breeds.
In the United States little has been done in the way of scientific duck breeding. Yet the best commercial flocks are remarkably uniform in the size and quality of the market birds, and remarkably efficient in fattening under good management; in 12 weeks they increase their weight 50 times. This uniformity may be in part due to the small number of Pekins in the original importations, from which nearly all the ducks of this breed are descended. As compared with chickens, the degree of inbreeding would be comparatively high, which would tend to make for homogeneity.
Duck breeders still rely entirely on their ability and experience in selection, and have not resorted to trap nesting, progeny testing, and the keeping of individual pedigree and production records. Mass matings are used exclusively, and the breeding birds are kept for only one laying season, on the ground that young birds lay earlier and are more prolific. These conditions preclude the keeping of individual records or the making of individual tests. Experimental inbreeding or cross-breeding is negligible or lacking, though the Aylesbury is sometimes crossed with the Pekin in England, and the mule duck, a cross of the Muscovy and the common domestic duck, is occasionally seen in this country.
In England trap nesting is practiced with the egg-laying breeds, and in the 16 years since individual records have been kept there has been great progress in improving egg production. The highest individual production runs over 360 eggs in a year, and there are many records of over 300 eggs. In egg-laying contests the average production per pound of body weight is much greater than is the case with chickens.
Ducks offer a virgin field for poultry-breeding research, especially Mm the inheritance of meat characters, since they are chiefly used for meat in this country. The same general principles should apply here as apply in the case of chickens. Research of this nature, however, is not likely to be undertaken except in response to definite needs felt and expressed by those concerned in the industry.
Breeding and genetic research is important in two ways in the conservation and improvement of fur resources. First there is the problem of maintaining the wild fur resources of the United States. There was a time when this country was the world’s chief source of furs. Fortunes were made in the fur trade. Partly because of the lavish exploitation of fur animals, we no longer supply more than a third of our own needs. Meanwhile our demand for furs has increased, and little is done to conserve the fur animals we have left. An intelligent conservation policy requires, among other things, much more knowledge than we now have of the breeding habits and gestation periods of the animals in the wild. Studies of the marten made by the Bureau of Biological Survey, for example, show that this animal has a gestation period of 9% months. This means that under any ordinary system of closed and open seasons, it would rapidly become extinct; in order to save the martens, it is necessary to prohibit trapping for several consecutive years. Similar accurate information on wild fur animals other than foxes is practically nonexistent.
The second need for research is in connection with the production of fur animals on farms. This is a rapidly growing industry in which an increasing number of farmers engage as a part-time enterprise. It is relatively very young, but it has now passed the early speculative stage and is settling down to a healthy basis. In 1923 the total value of silver fox pelts was less than $820,000; in 1936 it was over $8,000,000.
Fox farming has reached the stage where it needs the same kind of help from science that has long been given to other livestock industries. There is little in the way of a well-thought-out or scientifically tested procedure in present breeding practices. At the same time, fur color, which is the primary factor from the market standpoint, lends itself particularly well to inheritance studies and genetic analysis. A research project begun in 1928 by the Bureau of Biological Survey indicates what may be done in this direction. That study was an attempt to find out how the major types—the red fox; the standard silver fox, a mutation that occurred in Canada; the Alaska silver fox, a mutation that occurred in Alaska; and the cross fox, a hybrid between red and silver—behave in inheritance. Two pairs of genes, A, a, B, b, apparently accounted for these variations in color; and in breeding experiments, supplemented extensively from records of matings made by fox farmers, this genetic hypothesis worked out with remarkable accuracy, so that it was possible to tell, by referring to a genetic chart, just what results any given combination would give in a large population.
The Bureau is now engaged in a project to determine the inheritance of degrees of silvering in the pelts, since this is the fundamental basis of market classes. Both studies, however, have been limited by the small amount of funds available for such projects. There is need for more extensive research on this and other aspects of fur animal breeding by public agencies, both Federal and State.
The individual bee has such a painful and distracting way of making its personal importance felt that probably few of its victims have ever realized that in the United States bees are also the nucleus of a 35-50-million-dollar beekeeping industry, or that they give us much of our food supply by fertilizing blossoms. Both facts underscore the importance of breeding better bees.
The bee breeder, however, has a peculiar and in some respects an exceedingly difficult task. For example, he is confronted by at least five factors not faced by the breeder of other farm animals. (1) Bees mate in midair, and until recently it was impossible to make controlled matings, except in an uncertain way through the use of isolated mating yards. (2) The drone is produced by virgin birth and therefore receives its inheritance entirely from its mother. (2) The drone dies immediately after mating, and the queen mates only once in her lifetime; therefore their use in line breeding has been impossible. (4) The worker bee, which does the work of gathering and storing honey is not fully developed sexually and therefore cannot be bred for a direct study of its inheritance, although it does at times produce males by virgin birth. (5) Identification of individuals and even races of bees often depends on very small points, which must be measured by special methods.
As a groundwork for breeding, it has been necessary (1) to study sex physiology and functioning, and (2) to develop physical measurements that can be used for identification.
The greatest hurdle was passed when methods were developed within recent years for artificially inseminating queens. This is now done in three ways—by taking spermatozoa from the male and introducing them into the female with a tiny syringe; by bringing about a compulsory mating between a queen and a drone, both held under constraint; or by removing the sex organs of the drone and inserting them in the queen. The first two methods were developed in the United States, the last in the Union of Soviet Socialist Republics. All three now involve the use of a microscope and delicate instruments. A limited approximation to line breeding may even be made by removing spermatozoa from a fertilized queen may even be introducing them into a daughter of the drone from which they originally came.
It remains to develop a technique for controlled mating under more natural conditions.
Progress has also been made in cataloging traits that will be useful in identifying individuals, tracing the effects of inheritance, and measuring colony behavior.
Meanwhile, without waiting for the uncertain appearance of useful mutations or for an exhaustive study of inheritance, the bee breeder is in a position to go ahead toward the goal of producing a bee better adapted to the needs of agriculture. He has several traits available in the germ plasm of the common black, Caucasian, Carniolan, Italian, and Cyprian races that it should be possible to combine—long tongue to reach deeper sources of nectar, gentleness, the tendency to make white comb cappings, reluctance to swarm, resistance to European foulbrood and to common hive enemies, industriousness, and uniformity of body markings.
Some interesting but inconclusive work has been done on the cytology of the honeybee. Genetic research has been scanty, but the inheritance of some characteristics has been studied, dominance and recessiveness has been determined for a few factors, and a few linkages have been worked out. It is known that Mendel worked with honeybees in his effort to determine the fundamental laws of inheritance, but unfortunately his notes have been lost.
Reproduction by means of sex involves the union of two cells, a male and a female, each of which carries a set of chromosomes containing large numbers of genes that determine hereditary characteristics. For example, when two parents with contrasting characteristics have been bred pure, the first generation resulting from their union has all the chromosomes and therefore all the genes of both parents, If a plant of this generation is selfed (the closest possible inbreeding), the characteristics of the original parent will begin to assort or segregate into groups among the offsprings of the second generation. The chromosome mechanism is such that all possible combinations come together if the number of second-generation offspring is large enough.
Thus beginning with the second generation, most of the progeny are not like either original parent but have different combinations or groupings of characteristics from both of them. In this wealth of new combinations of genes derived from two selected individuals, the breeder finds the particular combination he is looking for—or something that approximates it.
The segregation of characteristics occurs in definite ratios, first discovered by Mendel. They can be worked out mathematically from the fact that all possible combinations occur in a large number of progeny, but Mendel worked them out by observation and thereby found the clue to this fundamental law of inheritance.
A knowledge of the segregation ratios gives the breeder the clearest possible insight into the actual behavior of characteristics in inheritance, and in addition these ratios are of practical value in a number of ways. There are a great many different ratios because the effects of dominant and recessive genes, and various gene interactions, bring about many modifications of the basic numbers. The typical examples can be readily understood by patiently following, step by step, what actually happens in inheritance.
Other concepts constantly used by the breeder include linkage (the location of certain genes in the same chromosome), crossing over (the exchange of segments between two paired chromosomes), sex linkage (location of genes in the sex chromosomes), and mutations. All of these help to explain what actually occurs in nature and to define what the breeder can expect and what he cannot expect to accomplish.
Animal breeding does not lend itself to the same kind of neat and definite analysis for several reasons: (1) Selfing is impossible, and the closest inbreeding does not approach that in plants. (2) More progeny are required for many genetic analyses than can usually be obtained with animals. (3) Most valuable characteristics in animals are quantitative (amount of milk produced, etc.), and such characteristics usually depend on relatively large numbers of genes interacting in complex ways. Nevertheless, there is an abundance of proof that animal inheritance works just like plant inheritance, and the basic concepts of genetics have been of enormous value in clarifying and improving animal-breeding methods. Even though the animal breeder will probably never be able to make the fine-spun analyses possible for the plant breeder, the newer knowledge of genetics is already reflected in animal-breeding practices, and it will undoubtedly make for more certain and more rapid progress, and fewer costly errors, on the part of those who will take the trouble to understand it.
When plants are reproduced by means of cuttings, buds, tubers, tunners, rattoons, or other vegetative parts, the breeding situation is different than when reproduction is by means of seeds.
A seed results from the union of two cells, male and female. Even if these come from the same flower or the same plant, many of the male and female cells will contain different chromosomal material unless the plant has been bred pure so that all its male and female reproductive cells have identical chromosomes. The differing chromosomes will be divided up among the progeny in such a way as to produce different types of individuals.
In reproduction by means of vegetative parts, there is no union of sex cells, and each new plant has precisely the same chromosomes as the plant from which it came. Exact copies of the original parent can be reproduced for any number of generations. Winesap apple trees have been reproduced by budding or grafting for many generations, and theoretically every Winesap tree today is exactly like its original ancestor of 200 years ago. Thus by the use of vegetative reproduction, all the trouble of ‘purifying’ a strain is eliminated. Even the most mixed hybrid reproduces true to type. When this method is feasible, then, it is often a valuable short cut, especially where is difficult—as in the case of many forest trees—to obtain true-breeding material from seed.
But occasionally the new individual is not exactly like the parent. Rarely, there are mutations in one or more genes in a vegetative cell, or some unusual behavior of the chromosomes, that make a part of the plant different from the rest. Usually this occurs only in one ease out of several thousand. When the new form is valuable—as has been the case with some of the bud mutations of tree fruits—it too can be multiplied by means of vegetative reproduction.
On the other hand, this very ease of exact reproduction has limitations. The true genetic make-up of the breeding material is neglected; there is no need to know it, as there is in inbreeding and cross-breeding. Yet it is through the diversity of forms brought about by combining different chromosomal material that the modern breeder gets valuable additions to our economic plants. If he desires to make planned improvements, he must resort to seed production even with those that normally are reproduced by vegetative means. This has been amply proved, for example, in the case of potatoes and strawberries. By. combining chromosomes, the breeder deliberately creates what he desires. When he uses vegetative mutations, he merely waits for nature to produce something that will be useful to him, trusting to trained observation to find it.
Do plants reproduced by vegetative means for many generations tend to run out or be weakened for the battle of survival? This has long been a popular belief. It may be said flatly that there is no real evidence that running out occurs. Where plants seem to run out it has been found in every case that the deterioration has been due to a virus disease or some other definite cause.
By studying the architecture of the molecule, chemists have been able to achieve marvelous results in synthesizing nature’s products in the laboratory. How far geneticists may be able to go in this direction is not yet known, but new advances seem to be foreshadowed in the researches now being made on nature’s methods of juggling chromosomes. Intensive study of the jimsonweed has been fruitful of knowledge in this field that may prove to have significant applications to breeding work with plants of economic value.
The present-day Mendelian analysis of inheritance, with its dominant and recessive traits, assumes that chromosomes go in pairs in the body cells. It is now known that they do not by any means always go in pairs. Rarely, there is only one of each kind instead of a pair. More frequently there are three or four of each kind, or even more. In some genera of plants, this arithmetical multiplication of chromosomes may run in a regular series, different species being characterized by different numbers of chromosomes in the set, though all the species in the genus have the same number of sets. This regular increase gives rise to what are called balanced chromosomal types, since the balance between the sets is maintained in spite of the additions.
But there are also unbalanced chromosomal types in which only a single set has an extra chromosome or chromosomes added to it. The balance within the cell is then disturbed; there is an excess of the material contained in the extra chromosome. Sometimes a complete extra chromosome or two is added to a set. Sometimes two identical half-chromosomes are added, joined together like a worm with a head at each end and the tails missing. Sometimes the addition is half of one chromosome and the opposite half of a chromosome from a different pair, joined together like a head and a tail from different worms. And so on.
Detecting this kind of jugglery within the cell might be interestingbut academic if it were not for the fact that chromosomes carry the determiners of hereditary characters. Careful observation in jimsonweed shows that each of these changes results in specific alterations in the characteristics of the plant, both qualitative and quantitative. Large numbers of such changes have been classified and correlated with the addition or subtraction of whole chromosomes or different parts of chromosomes. The differences between races of jimsonweed in different parts of the world have been found to be due to rearrangement of chromosome material. In this way new kinds of chromosomes have been produced, which have been used in building up new kinds of jimsonweeds. Types can be arranged in a regular series, and what effects will be produced by deleting or adding certain chromosome material can be predicted in advance.
From a practical standpoint, the significance of this lies in a possible increase in the controlled synthesis of plants of desired types. It suggests a somewhat different operation than that based on the usual analysis of unit factors alone. Cytological examination shows that many of our most valuable plants are characterized by unusual chromosome numbers of one kind or another. Can we repeat these deliberately, or bring about new and different additions and sub- subtractions of chromosome material that will have significant effects? The experimental production of extrachromosomal types in jimsonweed is promising. Not the least interesting part of it is the fact that by suitable laboratory treatment of living cells such changes in chromosome material can be made to occur far more frequently than they do in nature.
The modern science of genetics is a fusion of several sciences and practices that for a long time developed separately—animal breeding, plant breeding, cytology, or the science of the microscopic cell, and certain branches of mathematics. If today men not only dare to dream of emulating and surpassing nature by creating new, improved forms of life, but actually do it on an ever-increasing scale, it is because they have a rich store of facts and theories on which to base their work—facts and theories contributed by patient researchers in many countries over many generations.
Both animal en plant breeding of a practical nature, of course, are very old, but all of the early work was hit-or-miss and uncertain, since it was not based on adequate knowledge. The first great milestone in modern genetics was the announcement by Camerarius of Germany in 1694 that plants reproduce by the union of male and female cells. This suggested deliberately uniting two different kinds of plants and was followed by the hybridization work of Fairchild in England about 1717, and of many others after him. It was not long (1727) before hybridization was put to commercial use by the Vilmorins in France, and by 1840 they were actually using a kind of progeny test. In 1859 Darwin put biological science on an experimental basis with his Origin of Species, and in 1866 Mendel in Austria, worked out the mathematical laws of dominance, recessiveness, and segregation, previously observed but not interpreted by other workers. Mendel’s paper remained unnoticed for many years, but meanwhile others were hot on the trail of the same conclusions, When his work was rediscovered in 1900, it gave a tremendous impetus to research and practical breeding alike. Shortly after this (1902-03), the observed phenomena of heredity were definitely and finally linked with activities within the cell.
The development of knowledge of the cell goes back at least to the time of Leeuwenhoek in the Netherlands, who first discovered the world of the-microscope (around 1677). In 1838-39, Schleiden and Schwann in Germany generalized that all bodies are made up of cells; 10 years later Hoffmeister in Germany actually saw chromosomes. In 1864, Nigeli in Switzerland was attributing the control of heredity to solid particles in the cell—an idea finally clinched by Weismann in 1892, after Haeckel, Strassburger, Flemming, Von Beneden, and others had developed more knowledge of the cell nucleus. From this time on the study of chromosome phenomena proceeded rapidly through the work of many cytologists, up to our own day when genes are accepted as the basis of inheritance and more and more of the facts of heredity are being checked against observed happenings in the cell nucleus. These developments have contributed also to an understanding of animal breeding, which on the practical side goes back through the work of Bakewell, the Collings, and others of a century ago, to Mago the Carthaginian, who in pre-Christian times developed the first known score card for livestock judging. Without mathematics, much of this knowledge would be unusable, and the work of many mathematicians has contributed to the exact interpretation of phenomena and to the practical application of theory.
Outstanding among recent developments are the identification of hundreds of genes in various organisms; the "mapping" of genes on chromosomes by genetic studies, and cytological proof of the actuality of these concepts; the use of the pomace fly for extremely fruitful genetic investigations; an understanding of many complex gene interactions that modify the original Mendelian laws; an increasing body of knowledge about chromosome behavior, which promises to open up new possibilities of practical control in breeding; and the beginnings of knowledge, through the use of X-rays and other forms of wave energy, of how basic changes in genes and chromosomes are brought about, so that controlled genetic change becomes a speculative possibility.
The most recent developments indicate that new researches in biological chemistry may in their turn throw light on some of the many unsolved secrets of the gene and its control of heredity.