[starts on page 703 of the 1937 USDA Yearbook in the Stone Fruits chapter -ASC]


In THE United States, as well as in Europe, the plum has long been recognized as one of the most delicious of fruits, and among the stone fruits it ranks next to the peach in commercial production. Many of the varieties of plums now cultivated in the United States have been introduced from many foreign countries, and when these are added to the native varieties they give plums the largest number and greatest diversity of kinds and species among the stone fruits. The fruits exhibit a wide range of size, flavor, color, and texture. The plants vary from small shrubs with drooping branches to trees of large size with large, upright branches, and some have great beauty as ornamental plants (3, 19, 34).

The common European plum, known botanically as Prunus domestica L., appears to have originated somewhere in southeastern Europe or western Asia, probably in the region around the Caucasus and the Caspian Sea. Although it is called the European plum, De Candolle, who summarized the history of these stone fruits, is very doubtful whether P. domestica is indigenous to Europe. According to the earliest writings in which this plum is mentioned, the species dates back some 2,000 years. Another Old World plum species, probably of European or Asiatic origin, is the damson plum, P. insititia L. This species seems to antedate P. domestica, as is suggested by the finding of damson plum pits in ancient ruins. The ancient writings connect the early cultivation of these plums with the region around Damascus.

It is not known just when European plums were introduced into North America, but probably pits were brought over by the first colonists. It is reported that plums were planted by the Pilgrims in Massachusetts, and importations were made by the French into Canada. These European plums have done remarkably well in the New World, and today they constitute the most important group grown commercially for canning and drying.

The native American plums were doubtless used for food by the Indians long before the white man set foot on the shores of this continent. Reports of early explorers mention the finding of plums growing in abundance. According to the descriptions of the early settlers, these plums were inferior to the domesticas of the Old World in quality, so that the colonists soon began importing varieties from Europe. As a result, European plums soon became predominant in home fruit gardens as well as commercial orchards in the northeastern United States.

Another important species of more recent introduction into North America is the Japanese plum, P. salicina Lindl., which was domesticated in Japan and was introduced into the United States about 1870.


Cultivated varieties of at least 12 species of plums are to be found in American orchards or growing in the wild, but most of the important commercial varieties are confined to 4 of these species. A wealth of types, varieties, and species is available for the fruit breeder. he best known and most important of these groups are varieties of Prunus domestica, the European plums and prunes. Unfortunately they are not well adapted to regions with hot, dry summers or dry, cold winters. They are at home in the northeastern United States; in sheltered sections along the Great Lakes and in the Intermountain and Pacific Coast States they are at their best, as is evidenced by the extensive production of fresh fruit and dried prunes in this region. The European plums have been under domestication longest, and the fruits are notable for large size and attractive appearance. They vary in color from the green and golden yellow or the Reine Claude (Green Gage) and Yellow Egg groups to the red and dark purple of the Lombard and Italian Prune (fig. 11). Italian Prune, Agen, Sugar, and Imperial Epineuse constitute an important group of European plums with firm flesh and high sugar content suitable for use fresh or as dried prunes (fig. 12). - Other varieties, such as Tragedy, Reine Claude, Bradshaw, and Golden Drop, are used principally for canning and dessert plums.

Figure 11.—Types of fruit in the group of Prunus domestica: A, Reine Claude, a high-quality plum of the Green Gage group; B, Bradshaw, formerly an important variety in the Lombard group of reddish plums used for canning and dessert, but being replaced by better varieties produced as a result of hybridization and breeding; C, Diamond, a blue plum of the Imperatrice group. The varieties of this group are of medium size, dark blue in color, with a heavy bloom.

Figure 12.—Some of the most important varieties of Prunus domestica used for making prunes: A, Italian Prune, showing the shape of the fruits in the prune group; B, some varieties that produce large prunes when dried.

The damsons (Prunus insititia) of the Old World are quite different from the domesticas. The trees are more upright, compact, and dwarfish, the leaves and flowers are smaller, and the fruits are small, round and quite tart, so that they are especially suitable for preserves and jams. Varieties of this group are hardy, vigorous, and productive, and the trees make good stocks for other species, being adapted to a wide range of conditions and thriving even when they are neglected. The Shropshire (fig. 13) and French are important blue damsons in this country, while the yellow Mirabelles are popular in France. The group as a whole has been overlooked in breeding investigations.

What is Susan Collins? (damson in distress?)
Figure 13.—Shropshire, one of the most important varieties in the damson group of Prunus insititia. This small blue plum, like others belonging to this group, is used principally for preserves.

The Japanese plums (Prunus salicina) are relatively new to North America, but in the short time since their introduction they have been widely planted and now rank second to the domesticas in commercial production. The trees are more spreading in habit than the domesticas or damsons, and in leaf and fruit characters they are very different, resembling the native American plums. The fruits are very attractive and are characterized by a yellow ground color overlaid by various shades of red. In some varieties, the flesh color is a striking red, whereas fruit of the domesticas and damsons is green or yellow. Some recent hybrids of the salicina group (fig. 14) show distinct superiority in flavor and in commercial possibilities over the early importations. Varieties of this group appear to be widely adapted in this country except in the very coldest climates. While the quality is not equal to that of the best domesticas, the fresh fruit is delicious in its blend of flavors. The varieties cross readily with one another and with the native americanas. Among the first Japanese plums grown in this country, Kelsey, Burbank, Abundance, and Satsuma are typical. The trees are hardy and productive, and they tolerate a variety of soils as well as climatic conditions. They blossom early, and the flowers are sometimes killed by late spring frosts.

Figure 14.—Plum hybrids. A, Prunus salicina hybrid, variety Apple. This red-fleshed variety illustrates the round shape of the varieties of this species. B, America, a hybrid between P. munsoniana and P. salicina. C, Hybrid resulting from a cross of the purple-leaved plum P. cerasifera var. pissardii with P. salicina variety Abundance.

Among the plums native to North America are varieties that are different in fruit and tree characters from the plums of Europe and the Orient. Botanists have divided the native American plums into a number of species and subspecies. Many of them have numerous characteristics in common, so that they overlap somewhat in present horticultural groups and classifications. Prunus americana Marsh., the most important of the native species, has a wide range of adaptation in this country, extending from Maine to Florida, westward to Utah, and northwestward into Manitoba. The tree is small, not as vigorous as the European, and it has rough, shaggy, grayish bark. The fruit is red, reddish yellow, or reddish orange, of pleasant flavor and good quality, but it has a thick, tough skin, and the flesh clings to the pit. De Soto and Weaver are among the typical cultivated varieties of americanas.

Other American species of minor importance from a commercial standpoint but of interest to the fruit breeder are the native varieties of Prunus hortulana Bailey; the Chickasaw plum, P. angustifolia Marsh.; and the wild-goose plums, P. munsoniana Wight and Hedr., of the southeastern and south-central United States, of which Wild Goose and Robinson are important varieties (8, 32).

Other species of plums growing in North America are the Canada plum, Prunus nigra Ait., which is adapted to the north-central United States and Canada; the small beach plum, P. maritima Marsh., which grows along the eastern seacoast; and the western or Pacific plum, P. subcordaia Benth., which grows east of the Coast Range in southern Oregon and northern California.

Finally, mention should be made of the myrobalan plum (Prunus cerasifera Ehrh.), a native of Europe, and the Simon or apricot plum, P. simonii Carr., a native of China. The myrobalan plum has been used a great deal in this country as a rootstock. Varieties of P. cerasifera and P. simonii are noted for their ornamental foliage.

This great collection of varieties and species affords an excellent opportunity not only for studying genetic relationships but for the development of new varieties by breeding. The study of the inheritance of characters in plums has, however, not been very extensive. This may be due in part to the fact that many varieties of plums are self-unfruitful; that is, they do not set fruit with their own pollen. This presents a problem to the fruit grower as well as to the plum breeder. It is, of course, impossible to obtain an inbred progeny to study the inheritance of characters if the blossoms cannot be selfed. Fortunately for both the breeder and the fruit grower, fruits can be obtained by cross-pollination, and not all varieties are self-unfruitful.


It is a well-recognized fact that plum culture in North America has gradually been declining during the last 20 years. The reason for this is the failure to keep pace with the demand for fruits of high quality. Varieties that were satisfactory 25 to 50 years ago in most cases do not appeal to persons who have a taste for fruits of high quality. However, many varieties are still prized in the home garden even though they are not profitable to the large producers.

An important objective of any plum-breeding program should be the production of varieties of higher quality adapted to the various fruit regions of the country. None of the domestica plums of high quality can be grown satisfactorily south of Virginia or in the vast regions of the southwestern and south-central United States. Native American species grow in this part of the country, but their adaptability must be combined with the higher quality of other varieties and species. Work has been started in this direction, but it has met with failure because domestica and americana varieties have different chromosome numbers, and so far crosses between them have not yielded viable seedlings.

Further study is also needed in the direction of artificially increasing desirable mutations in plums. In a few instances desirable bud sports have been discovered, and careful search should be made to locate others.

In addition to high quality, consideration must be given to vigor, hardiness, and productiveness. Much has been accomplished in developing and selecting winter-hardy varieties for the Great Plains region. Similar work is needed to develop varieties adapted to regions with hot, dry summers.

Genetic and cytological studies are of first importance in initiating a plum-breeding program. Among the self-compatible varieties there is a wealth of valuable material that can be used as foundation breeding stock. Even before methods are developed for increasing fruitfulness in crosses between species, there is opportunity for research on the material within many of the plum species growing in this country.


The methods of breeding that have been described for the peach apply equally well to the plum. The breeder is confronted with the same problem of protecting the emasculated flowers in order to lessen damage to the pistils. With varieties known to be completely self- incompatible, emasculation is of course unnecessary, and time can be saved by omitting this operation.

The problem of seed germination and the production of new seedlings likewise confronts the plum breeder. The seeds from many crosses prove nonviable, and methods need to be worked out whereby a greater percentage of seeds can be made to grow.


The first work on plum improvement in this country consisted of attempts to obtain better strains of the native American plums by domesticating seedlings and selecting those most promising for size, flavor, and productiveness. The most extensive work in this direction. seems to have been started by H. A. Terry, of Crescent, Iowa. From about 1860 until the time of his death in 1909 he had originated over 50 varieties from native species. While there is little information available as to the breeding methods or parents used, it is certain that he produced more new varieties than any private breeder since his time. Some of the more important varieties introduced by him are Gold, Hawkeye, Hammer, Downing, Crescent, and Terry.

Work on the breeding of plums was begun by C. G. Patten, a private breeder and a contemporary of Terry in the same State, at Charles City, Iowa, in 1867. He was impressed by the great number of native plums found growing in the wild, became interested in domesticating some of these, and selected the best for the prairie and upper Mississippi Valley regions. Hardiness or ability to withstand cold winters was a factor to be considered in the selection of varieties for that region. He worked with the American species. One of his best selections was tested by the Iowa Agricultural Experiment Station and was introduced as the Patten plum.

Beginning about 1870, J. W. Kerr, of Denton, Md., began the study and testing of a large number of varieties of plums. He likewise was interested in developing new varieties from native plums. Among the varieties introduced by him are Choptank, Sophie, and Maryland.

In California, Luther Burbank began his plum-breeding work about 1880, at Santa Rosa. He introduced and produced many desirable types. Among the important varieties he developed from seed imported from Japan are Burbank, Abundance, and Satsuma. He was particularly interested in the Japanese types and did much to popularize the varieties of this species in California, and to lay the foundations for their later testing and use as important commercial varieties in that State. He likewise made a number of crosses between Prunus salicina and other species, producing Climax, Bartlett, and Wickson from P. salicina X simonii, and America (fig. 14) and Golden from P. munsoniana X salicina. Other varieties introduced that have been grown commercially in California are Giant, Splendor, Standard, Santa Rosa, Formosa, and Gaviota.

Hedrick and associates (19, p. 170-171) make the following comment on Burbank’s work:

One cannot briefly catalog the new forms of plants that have gone forth from his private place in California; they must number well into the hundreds; his biographer, in 1905, said that Mr. Burbank has worked with over two thousand five hundred distinct species (Harwood, W. S., New Creations in Plant Life I, 1905). Among these have been practically all of the species of plums now under cultivation, from which have been obtained, according to Mr. Burbank, hundreds of thousands of plum-seedlings of which the breeder has selected a score or more of very distinct sorts, all interesting and a few of them very valuable. The many other fruits, flowers and forage plants which Mr. Burbank has sent out, each involving the handling of countless seedlings, cannot be mentioned here. Nor can his methods and results be discussed, except to say that in them he is a unique figure in plant-breeding and that they have been such that he has exercised a power influence toward the improvement of plants. The practical results of Mr. Burbank’s work have been as great or greater than those secured by any other person in plant-breeding, yet they have been magnified out of all bounds in the popular press and his work has been caricatured by calling the man a wizard and ascribing to him occult knowledge. Of the plants introduced by Mr. Burbank the proportion of really valuable commercial ones seems now to be small, put what he has done cannot be measured by money values; he has awakened universal interest in plant-breeding; has demonstrated that things unheard of before his time can be done with plants; and, all in all, his contributions in new forms of plants to horticulture and agriculture, in their intrinsic and educational value, make him the master worker of the times in improving plants.

Millard W. Sharp, of Vacaville, Calif., in more recent years has produced and introduced several plum varieties. The method he used was to top-work many varieties into a single tree, allow free crossing, plant the seed, and make intensive selection of the resulting seedlings. Of the varieties he introduced, Sharky and Becky Smith have attained commercial importance.

Plum-breeding work has also been undertaken by Albert F. Etter and August Etter at Ettersburg, Calif. In recent years they have used as parents for hybrids Wild Goose, Marianna, Golden Drop, Agen (French prune), Japanese varieties, and Sierra, a peculiar domestica type that grows wild in Trinity County, Calif.; two wild native plums from Mongolia, and the native plums of Kansas. In all, this includes about a dozen species. The outstanding ability to produce new forms shown by the Sierra, the Kansas, and the Trinity plums is of particular interest. The Sierra hybrids exhibit wide variations in tree and fruit characters. These are under test at the present time, but no varieties have been introduced.

Harlan Rockhill, of Conrad, Iowa, has been engaged in fruit breeding since 1895. Among his recent selections are some promising plum hybrids from crosses of Waneta X Apex, Waneta X Moorpark, No. 10 X P. I. 78519, Waneta dwarf seedling X Apex X P. I. 78519. The last-mentioned cross is reported to be particularly hardy in wood and bud, having withstood temperatures of —26° to —36° F. during the winter of 1935-36. This variety and others are being tested further.

South Dakota
Work was undertaken at the South Dakota Agricultural Experiment Station in 1895 by Hansen (15) in an attempt to select American varieties of plum that would be satisfactory for the Great Plains region. Up to 1937 fully 10,000 native plum seedlings of Prunus americana had been grown in an endeavor to find native seedlings better in size and quality than those already grown. Wastesa, Yuteca, Zekanta, Huya, and Topa were selected and named. Yuteca is large; Wastesa is outstanding for size and quality. Hansen attempted to introduce quality into the native plums by crossing these into a number of other species such as peach, cherry, and apricot, as well as with other varieties of plum. The following is a list of crosses made, together with notes on the progeny:

Prunus besseyi Bailey (Bessey cherry or western sand cherry) X apricot plum P. simonii Carr. Not hardy, fruits sparingly. One variety only named but the trees have since been discarded.
P. besseyi X Japanese plum (P. salicina Lindl.). Progeny highly fertile, hardy, widely cultivated. Among varieties named are Opata, Sapa, and Oka.
P. besseyi X native plum (P. americana Marsh.). Two varieties named, Sansoto and Cheresoto, which are highly fertile.
P. besseyi X Apricot (P. armeniaca L.). Progeny very shy bearers.
P. besseyi X peach (P. persica). Flowers of hybrid (Kamdesa) were sterile.
P. americana X simonii. Three varieties named, Toka, Hanska, and Kaga, which are strong pollinators for other varieties. The fruit is fragrant, flesh firm, and of excellent quality.
P. simonii X americana. This cross produced Tokata: the fruit is large and of excellent flavor. The seedlings of this cross require cross-pollination.
P. salicina X americana. The progeny of this cross is highly fertile. Five varieties have been introduced and widely cultivated—Waneta, Kahinta, Tawena, Oziya, Tecumseh.
P. americana X salicina, the reciprocal of the former species cross, has yielded many choice hybrids which are self-fertile and interfertile.
Canada plum (P. nigra Ait.) X P. salicina. This combination has yielded the varieties Cree and Pembina.
P. salicina X nigra has given the variety Ojibwa.
From Canada plum, Prunus nigra, pure selections have been made and introduced as Assiniboin and Winnipeg.
Since 1895 selections have been made from over a million seedlings of Prunus besseyi. The thirteenth generation has now fruited.

New York

At the New York (State) Agricultural Experiment Station, Geneva, plum breeding was started as early as 1893, when a few open-pollinated seedlings were grown. Under test the seedlings proved to be of no commercial value. From 1908, when the first crosses were made at the New York station, up to the present time, 78 varieties, 6 seedlings, and 7 United States Department of Agriculture introductions have been used in breeding work, and 546 crosses, 16 selfs, and 26 open pollinations have been made. Only 519 seedlings have been planted in the orchard. The set of seed has not been high, and there were serious losses between the time of harvesting the seed and planting. Considerable difficulty has sometimes been experienced in getting the seeds to grow. A few Japanese plums (Prunus salicina) have given seedlings, but no seedlings have been obtained from the early-maturing European or domestica group.

It has been the experience in the plum-breeding work at Geneva that it is difficult to obtain large quantities of seed from hand- pollinated trees. The flowering season is usually brief and there is often a high mortality of blossoms. It has been suggested that the use of tents and bees for pollination would be the economical method for securing large numbers. The comparatively few seedlings that have fruited indicate that it is not difficult to make rapid progress in plum improvement. The large-fruited, attractive, poor-quality Grand Duke has given promising new varieties when crossed with high-quality Golden Drop and Agen. Imperial Epineuse and Pearl have also imparted good quality to a high degree in crosses. The varieties that have been used most extensively and the number of times they have been used are: Abundance 23, Agen 23, Albion 8, Archduke 8, Beauty 17, Burbank 57, Clyman 11, Formosa 13, Golden Drop 8, Grand Duke 23, Hall 12, Imperial Epineuse 30, Jefferson 8, Miller Superb 10, Oullins 22, Reine Claude 19, Rivers Early 12, Santa Rosa 16, Shiro 10, Stanley 16, Tragedy 8, and Yellow Egg 28. A list of plum varieties introduced by the New York station is given in table 4.

Table 4.—Plum varieties introduced by the New York (State) Agricultural Experiment Station
Variety introduced
When crossedYear introduced
AlbionGolden Drop X Grand Duke19081929Very late season
American MirabelleImperial Epineuse X Mirabelle19111925Home and roadside market
HallGolden Drop X Grand Duke19081925Home and roadside market
StanleyAgen X Grand Duke19131926Commercial market

The opinion is expressed by Richard Wellington that by intercrossing hybrids such as Hall, Albion, and Stanley, and by crossing them on high-quality plums such as Imperial Epineuse, varieties of better quality should be obtained. A large number of varieties and species of plums are grown on the grounds of the New York station as basic material for the production of better varieties.


The California Agricultural Experiment Station at Davis has grown a large number of varieties of plums on the station grounds. These have been used in studies on pollination and variety behavior under California conditions. Because of the demand for improved varieties of plums, breeding work was started in 1934. Poor germination of plum seeds has been an important factor in slowing down the production of seedlings. All the species of plums grown in North America, together with some miscellaneous species, are being utilized. A complete list is given in the appendix. Genetic and cytological work on interspecific crosses is under way.


At the Iowa Agricultural Experiment Station a large number of plum crosses have been made, using Prunus americana, P. salicina, P. domestica, and P. maritima; also P. armeniaca. Interspecific hybrids between P. americana and P. salicina are grown, and 180 trees resulting from crosses between species and varieties are now being grown in the nursery at Ames. These crosses were made during the period 1931-33. Varieties used as pollen parents and the number of times they were used are: Elliot 5, Hennepin 4, Japex 2, Monitor 2, Sapa 5, Waneta 6, and Anthony, Zumbra, Red Wing, and Burbank each 1. Crosses between the plum and the Russian and Moorpark apricots have been made. Greenhouse trees are being utilized in the breeding work with Prunus, and many hundreds of nonfruiting crosses not listed above have been made on them. The interspecific hybrids that prove to be fertile will be preserved for future crossing. The trees are brought into the greenhouse about January 10 and are ready for crossing about 3 or 4 weeks later.


Plum-breeding work at the Minnesota Agricultural Experiment Station was begun in 1889 at University Farm by S. B. Green, horticulturist. In the same year breeding work was also started by E.H.S. Dartt at Owatonna Tree Station, a branch station of the University. This work consisted of selection of open-pollinated seed from superior native varieties. More extensive and systematic work began in 1907 with the establishment of the present University of Minnesota Fruit Breeding Farm. Up to the present 20 varieties have been introduced— Anoka, Elliot, Ember, Golden Rod, Hennepin, La Crescent, Mendota, Monitor, Mound, Newport, Nicollet, Radisson, Red Wing, St. Anthony, Superior, Tonka, Underwood, Waconia, Winona, and Zumbra. They are of special interest for the upper Mississippi River Valley area because of their winter hardiness, but are worthy of testing in other sections also, and they should provide material for additional studies. Detailed descriptions of these varieties, their parentage, and the dates of introduction are given in the appendix, which also includes a list of the varieties now being used in further breeding studies.

A considerable amount of breeding material is available involving various species of native and foreign plums and other closely related species of stone fruits. Since winter hardiness is a primary requisite, all breeding material is subjected to severe field tests to determine its resistance to cold.

Federal Field Stations

A number of varieties and specific crosses of plum have been made in cooperative investigations by the Bureau of Plant Industry, United States Department of Agriculture, and Leland Stanford Junior University at Palo Alto, Calif. The following varieties and species have been used as seed parents: Agen, Anita X Sugar, Becky Smith, Burbank, Clyman, Duarte, Fremonti, Giant, Golden Drop, Imperial Epineuse, Improved French, Methley, Pond, Sergeant, Tragedy, Wickson, and Prunus bokhariensis Royle. In addition the following varieties have been used as pollen parents: Sugar, Gaviota, Formosa, Santa Rosa, Beauty, Satsuma, Standard, and Tunis. Two promising hybrids, Methley Wickson and Wickson X Santa Rosa, have been selected. The latter variety is a delicious plum, representing a particularly fine blend of flavors and ripening just after Santa Rosa. The tree is productive and in preliminary tests seems to be well adapted to California conditions. A complete list of plum hybrids produced is given in the appendix to this section.

At the Northern Great Plains Field Station, Mandan, N. Dak., more breeding work has been done with plums than with any other fruit except apples. Thousands of seedlings have been grown from the native wild plum and cultivated varieties. A great deal of variation is to be found within the Prunus americana species, and over 50 selections were made, some of which were propagated for a more thorough test. A few of these are ready for more extensive testing in the northern Great Plains area. Of late years a large number of Japanese hybrid seedlings have been grown. Hybridizing work has been in progress, using hardy P. americana and P. nigra varieties, these being crossed with Japanese varieties, domestica varieties, P. simonii, P. tomentosa Thunb., apricots, and cherries, and with such hybrid plum varieties as Waneta, Underwood, and Sapa. Some of the progenies are now bearing fruit, and a few selections have been made.


Plum breeding at the Horticultural Experiment Station, Vineland, Canada, was started in 1913. From 1913 to 1935, 4,240 seedlings were grown. Seeds were planted from 57 open pollinations and 35 crosses. Out of this number 16 had horticultural value. During the period 1931 to 1933, 860 seedlings were grown from crosses in which Imperial Epineuse was used as the female parent, and Grand Duke, Coe Fellenberg, and President have been used as pollen parents. The object of the cross was to produce a high-quality blue plum for the export trade.


Experiments with plums were begun at the John Innes Horticultural Institution in England by W. J. Backhouse and Crane (8) in 1911, to investigate the genetic composition of plum trees by raising selfed offspring. The characters studied were: (1) hairiness of shoots, leaf petioles, and fruits; (2) smoothness of bark and size and shape of leaves; (3) habit of growth of tree; and (4) bark and fruit color.

All the varieties of plums studied with hairy wood surface proved to be heterozygous for that character. Serrate leaf character proved to be homozygous in the Pershore variety, and crenate leaf margin homozygous in the Czar family. The irregular margin appeared to be heterozygous in varieties possessing this character.

Flesh color varied. Varieties in which yellow was the predominating flesh color have, when selfed, given seedlings with a green, and a wholly yellow flesh.

As to fruit size and shape, many of the differences were recognized as doubtless quantitative. The oblate fruit of Early Transparent, for example, and the pyriform fruit of the Pershore variety proved to be homozygous for these forms. With some selfed families, length and shape varied in the progeny.

Wellington (32) has carried on extensive investigations at the New York (State) Agricultural Experiment Station in breeding and genetic studies with a number of plum varieties and species. He found the oval fruit shape of Prunus domestica dominant to oblate. Thick bloom on the surface of the fruit is dominant to thin bloom. Yellow color is recessive to red, purple, and black. The freestone character is recessive to clingstone. Many varieties are heterozygous for the freestone character, freestones being obtained from the cling and semicling parents.

Some varieties of our domestica plums set fruit with their own pollen; others are partially self-incompatible, while a third group fail entirely with their own pollen. Instititia varieties grown in this country are self-fruitful. Nearly all of the varieties of the Japanese group are self-sterile.

Tufts has found the following important varieties of domestica plums to be self-unfruitful in California: Clyman, Tragedy, Imperial Epineuse, President, Standard, Sergeant, Washington, Jefferson, Quackenboss, Diamond, and Silver. Self-fruitful varieties were Agen, Giant, Pond (partially), Grand Duke (partially), California Blue, Yellow Egg, and Sugar.

The following Japanese and hybrid plums were self-unfruitful in California: Abundance, Burbank, Duarte, El Dorado, Formosa, Gaviota, Kelsey, Prize, Satsuma, Sultan, Upright, and Wickson. Methley, Climax, Beauty, and Santa Rosa are partially self-fertile. Formosa and Gaviota were also found to be interunfruitful. The Tragedy plum will fertilize several Japanese varieties but is not fertilized by them.

Crane and Lawrence (10) observed that certain of the domestica plums were completely self-and cross-incompatible, while others, such as President and Late Orange, were reciprocally incompatible but set fruit when pollinated with Green Gage (probably Reine Claude). Early Rivers, when pollinated by Blue Rock, set a full crop, while in the reciprocal cross only a few fruits set. Varieties such as Golden Drop, Coe Violet, and Jefferson, were found to be completely self- and cross-incompatible (9).

Incompatibility Due to Genetic Make-up

Experiments by a number of investigators, East (13), Lehmann (24), and others, have shown that sterility is determined by genes just as are morphological characters. East designated these genes S, and they form A multiple allelomorphic series, S1, S2, S3, etc. As in the case of other allelomorphs, any two may be carried by a given plant. While this concept is based on the results of studies with Nicotiana, it fits into the observations made on stone fruits and explains incompatibility in plums and cherries. The essential features of the genetic behavior of incompatibility is that pollen cannot function in the style of a plant carrying the same incompatibility factors as the pollen. Self-pollinations or cross-pollinations among individuals carrying the same sterility genes fail because either the pollen tubes grow so slowly that in normal cases they are unable to reach the ovules in time to effect fertilization, or the growth of the pollen tube is inhibited in the stylar tissue. Consequently, groups of individuals occur within which all cross- and self-pollination. fails to effect fertilization. Thus, individuals of the constitution S1, S2, cannot be fertilized by S1 or S2 pollen. If, however, such individuals are crossed by S3 S4, both the S3 and S4 pollen can penetrate the style of the mother and effect fertilization. It will be seen that the offspring from such a cross, allowing all combinations possible, will constitute four intrasterile, interfertile groups of the composition S1S3, S1S4, S2S3, S2S4.

With certain of our plum varieties, of either the Japanese or the domestica species, self-unfruitfulness occurs when those varieties carry a gene for incompatibility. Likewise, varieties would be cross- unfruitful if both parents carried the same genes for incompatibility.

Chromosome Numbers in the Plums

In the genus Prunus the basic chromosome number is 8. All the varieties examined among the myrobalan plums (P. cerasifera), American plums (P. americana), and Japanese plums (P. salicina) show the diploid number (2n) to be 16. Other species, notably the sloe (P. spinosa L.), have the tetraploid number or 32 chromosomes, and a still greater number (48) is found in the important groups of European plums (P. domestica) and the damsons (P. insititia).

Hybrids of Prunus domestica (48) X P. cerasifera (16), and P. insititia (48) X P. spinosa (32) have the intermediate chromosome numbers, 32 and 40, respectively.

According to Crane and Lawrence (10), the hybrids that they have obtained between Prunus domestica and P. insititia, both hexaploid, have always been completely interfertile; but from crosses between diploid and polyploid, and different polyploid forms, such as P. domestica X P. cerasifera and P. insititia X P. spinosa, fruits with viable seeds are rarely produced. Crosses between damsons and other varieties of P. insititia and P. domestica when attempted have always set fruit and developed good seeds freely. Wellington has also made many interspecific crosses. Crosses have been made successfully between P. domestica and P. insititia. With a large number of other interspecific crosses, however, involving P. domestica X P. armeniaca and its reciprocal; P. domestica X P. tomentosa, and P. domestica X P. americana, few fruits were obtained or the seeds failed to grow. Insofar as is known, triploid varieties of Prunus are found only as ornamentals, their degree of sterility being too high to enable them to be grown for their fruits.

Table 5.—Locations of plum-breeding work and names of workers in United States and other countries
State or country, institution, and locationEarly workersWorkers actively engaged at present
Agricultural Experiment Station, DavisE. J. Wickson, W. L. Howard, A. H. HendricksonW.P. Tufts, E. C. Hughes
U.S. Department of Agriculture, Davis-------------------------J. R. King
U.S. Department of Agriculture, Palo Alto-------------------------W. F. Wight
Iowa:  Agricultural Experiment Station, AmesS.A. BeachT. J. Maney
Minnesota:  Agricultural Experiment Station, University Farm, St. PaulCharles Haralson, M. J. Dorsey, W.S. Valleau, J. H. BeaumontW. H. Alderman, A. N. Wilcox
New York:  Agricultural Experiment Station, GenevaU. P. Hedrick, W. H. Alderman, M. J. DorseyR. Wellington, Olaf Einset
North Dakota:  U.S. Department of Agriculture, Northern Great Plains Field Station, MandanMax PfaenderWilliam P. Baird
South Dakota:  Agricultural Experiment Station, BrookingsN. E. HansenN. E. Hansen
Canada:  Horticultural Experiment Station, Vineland, Ontario-------------------------F. E. Palmer, G. H. Dickson
England:  John Innes Horticultural Institution, Merton-------------------------W.J.C. Lawrence
Australia:  Department of Agriculture, Sydney, New South Wales-------------------------H. Wenholz

Table 6.—Varieties used in plum breeding at the University of Minnesota
ParentagePeriod during which crosses were madeTotal seedlings grownSeedlings of horticultural valueApparent value of parents used
Assiniboin Open191520816Fair
Assiniboin X Surprise1925-27229
Reciprocal cross1926181
Burbank X Assiniboin1920-2626
Reciprocal cross1925-266
Burbank X De Soto1913433
Reciprocal cross1912271Fair
Burbank X Kaga1920-2523333Good
Reciprocal cross1920-2615
Burbank X Older192710
Reciprocal cross1923-2714
Burbank Open1923-26393Fair
Burbank X Prunus americana1913-2627928Good
Reciprocal cross1922-27701
Burbank X Red Wing1920191Fair
Reciprocal cross192021
Burbank X sand cherry1920722Fair
Reciprocal cross192110
Burbank [X] (sand cherry X Climax)192030
Reciprocal cross1921482Fair
Burbank X S. Dak. No. 271921-269
Reciprocal cross1924-26891
Burbank X Surprise1924-2613
Reciprocal cross1921-2610
Burbank X Wakapa19211
Reciprocal cross1912-21202
Burbank X Wolf1912-26776Good
Reciprocal cross1923-2728
(Burbank X Wolf) open191231
Compass X Burbank1912602Fair
Compass X Climax19121075Fair
Compass X Formosa1912371Fair
Early Red X P. americana191221
Elliot X Mendota1922-2725
Emerald X Assiniboin1920179
Emerald X Tonka1920-2130
Emerald X (Wyant X Gold)19245
Reciprocal cross192415
Omaha X Burbank1912394Good
Omaha X Santa Rosa1912232
Omaha X Winnipeg191220
(Pin cherry X sweet cherry) X sand cherry or sand cherry hybrid19128111Good
Red Wing X Assiniboin1920-21156
Red Wing X Kaga1920-23542Fair
Reciprocal cross19203
Sand cherry X Climax1912605Good
(Sand cherry X Climax) X Sapa1920211
(Sand cherry X Climax) X Tonka1920-2125
Reciprocal cross1920
Sand cherry X Formosa1912274Good
Sapa X Surprise192424
Satsuma X Compass191226
Reciprocal cross1912291
Shiro X P. americana1912214Good
Shiro X S. Dak. No.331913317Good
Reciprocal cross19121
Shiro X Winnipeg1912387Good
Reciprocal cross191211
S. Dak. No. 27 X Monarch1924-2650
S. Dak. No. 27 X October192423
October X S. Dak. No. 2719241
S. Dak. No. 27 X Santa Rosa1925-26917Good
Stella, open1912-15721
Tonka X Assiniboin1920-25209
Tonka X Red Wing192033
Reciprocal cross19203
Wakapa X First191245
Wakapa X P. cerasifera pissardi191228
Wakapa X Wickson192126
Reciprocal cross19213
Wakapa X Wyant191222
Winnipeg, open1915934Fair
Zekanta X P. americana1912202
Minn. No. 2 (Burbank X Wolf) X Burbank192418
Reciprocal cross192418
Minn. No. 6 (Burbank X Wolf) X Terry192321
Minn. No. 16 (Abundance X Wolf), open191230
Minn. No. 35 (Abundance X Wolf) X Burbank192010
Reciprocal cross1920975Fair
Minn. No.55(Abundance X Wolf) X No.57 (Shiro X Winnipeg)1924-2664
Reciprocal cross1924-2665
Minn. No. 55 (Abundance X Wolf) X No.63 (Shiro X Winnipeg)1924-2646
Minn. 55 (Abundance X Wolf) X No. 90 (Burbank X Wolf)211924872
Minn. No. 55 (Abundance X Wolf) X No. 104 (Burbank X ?)192425
Minn. No. 59 (Shiro X Winnipeg) X No.57 (Shiro X Winnipeg)1924-2764
Reciprocal cross1925-264
Minn. No. 62 (Shiro X Burbank) X No. 57 (Shiro X Winnipeg)1924-2563
Minn. No. 66 (Shiro X Wolf) X No. 65 (Shiro X Wolf)1924-2525
Reciprocal cross19251
Minn. No. 76 (Burbank X P. americana) X No. 62 (Shiro X Burbank1925-2623
Minn. No. 84 (S. Dak. No. 33 X Shiro) X No. 77 (Shiro X native)1924-2643
Minn. No. 90 (Tonka open) X No.55(Abundance X Wolf)1924111
Minn. No. 92 (Omaha x Wyant) X No. 74 (Santa Rosa X Bursota X Winnipeg)192495
Reciprocal cross19252
Minn. No. 92 (Omaha X Wyant) X No. 106 (Omaha X Santa Rosa)1924-2564
Reciprocal cross19256
Minn. No. 98 (?) X Winona, reciprocal cross1923242
Minn. No. 98 (?) X No. 96 (Zekanta X apricot) 192520
Minn. No. 106 (Omaha X Wyant) X No. 55192636

Table 7.—Plum introductions of the Minnesota Agricultural Experiment Station
VarietyParentageWhen crossed or seed collectedWhen introducedDescriptive notes (special value and superior characters)Estimated acreage now planted
Anoka (Minn. No. 118)Burbank X De Soto19131922Hardy; productiveSmall
Elliot (Minn. No.8)Probably apple plum X Prunus americana19071920Very hardy; productive; good quality; late season175 acres
Ember (Minn. No. 83)Shiro X S. Dak. No. 3319131936High quality; late season; long-keeping quality; exceptional adherence to treeSmall
Golden Rod (Minn. No. 120)Shiro X Howard Yellow19131923Vigorous tree; larger firm yellow fruit. (Variety a shy bearer.)50 acres
Hennepin (Minn. No. 132)Satsuma X P. americana19111923Hardy; productive; red fleshSmall
La Crescent (Minn. No. 109)Shiro X Howard Yellow19131923Very high quality; large, vigorous tree100 acres
Mendota (Minn, No. 5)Burbank X Wolf19081924Very large fruit; good qualitySmall
Monitor (Minn. No. 70)Probably Burbank X P. americana19121920Large, high-quality fruit; hardy regularly productive300 acres
Mound (Minn. No. 50Burbank X Wolf19081922Large size of fruit; productiveAll in scattered landscape plantings
Newport (Minn. No. 116)Omaha X Pissardii19131923An ornamental with purple foliage25 acres
Nicollet(P. avium X pennsylvanica)*19121925Dwarf, bushlike; fruit similar50 acres
Radisson (Minn. No. 157)P. salicina X americana19081925Early-maturing high-quality fruit; adapted to northern locationsSmall
Red Wing (Minn. No. 12)Burbank X Wolf19081920Large high-quality fruit; exceptional freestone250 acres
St. Anthony (Minn. No. 145)P. besseyi (or hybrid) X Satsuma19121923Very hardy and productive; red flesh50 acres
Superior (Minn. No. 194)Burbank X Kaga19201932Very productive and early bearing; fruit very large, firm, excellent quality100 acres
Tonka (Minn. No. 21)Burbank X Wolf19081920Very, productive; firm flesh; high quality300 acres
Underwood (Minn. No. 91)Shiro X Wyant19111920Very vigorous; hardy; productive; early ripening; excellent quality500 acres
Waconia (Minn. No. 10)Burbank X Wolf19081923Hardy; productive; quality only fairSmall
Winona (Minn. No. 80)P. salicina X americana19091922Hardy; productive; high quality; late seasonSmall
Zumbra(P. avium X pennsylvanica)*19121920Dwarf, bushlike; very productive; excellent culinary quality100 acres
* Open pollen parent is Prunus besseyi or a hybrid of this species.

Plum Hybrids Produced and Under Test in Breeding Investigations of United States Department of Agriculture and Leland Stanford Junior University at Palo Alto, Calif.
1921Agen X Anita
1931(Agen X Anita 18-31) x Imperial Epineuse
1929Agen X (Coe X Sugar)
1922Agen X Standard
1920Agen X Sugar
1931(Agen X Sugar 18-12) x Imperial Epineuse
1920Anita x Sugar
1931-32(Anita X Sugar) x Agen
1934Becky Smith & Tunis
1920Prunus bokhariensis X Methley
1921P. bokhariensis X Sugar
1920P. bokhariensis X Wickson
1934Burbank X Formosa
1932Burbank X (P. fremontii x cerasifera pissardii 11-3ξ)
1933Burbank 2010 X Gaviota
1932Burbank X Satsuma
1932Clyman 12010 x (Anita x Sugar 18-45)
1934Duarte X Santa Rosa
1933(P. fremontii X cerasifera pissardii 11-31) X P. bokhariensis X Methley 6-6)
1924-26Giant X Imperial Epineuse
1919Golden Drop (Coe) x Sugar
1931(Golden Drop (Coe) X Sugar) X Imperial Epineuse
1926Imperial Epineuse x Improved French
1924-26Imperial Epineuse X Tragedy or Agen
1926Improved French X Tragedy
1920Methley X Wickson
1935(Methley X Wickson 11-56) X Beauty
1932-33(Methley X Wickson 11-54) X Satsuma
1933(Methley X Wickson 11-57) X (Wickson X Santa Rosa 15-23)
1921Pond X Agen
1926Sergeant X Improved French
1926Tragedy X Clyman
1921Wickson X P. bokhariensis
1933Wickson 7-24 X (P. bokhariensis X Methley 6-6)
1921Wickson X Santa Rosa
1935Wickson X (Wickson X P. bokhariensis15-21)
ξ The hyphenated numbers following certain varietal names refer to row and tree locations.

Plum Material at the California Agricultural Experiment Station, Davis, Calif.ρ

Prunus domestica:
Agen (French)
Altharm [was this a typo and they meant 'Altham'? -ASC]
Austrian Prune
Autumn Compote
Bird Prune
Black French
Black Prince
Blue Rock
Burton Prune
California Blue
California Red
Champion (Burton)
Champion (Villa) [Actually, the link given to these plums may be incorrect for both- view with caution -ASC]
Clairac Mammoth
Coates 1401
Coates 1403
Coates 1414
Coates 1418
Crimson Drop
De Caisne
De Montfort
Double X French
Early Favorite
Early Golden Drop
Early Royal
Early Tragedy
German Prune
Golden Drop
Golden Prune
Golden Transparent [Is this the same as 'Transparent'? -ASC]
Grand Duke
Green Gage
Imperial [there are so many plums named Imperial or that have Imperial in the name, I'm not going to hazard a guess which one they meant. -ASC]
Imperial Gage
Italian Prune
Junction City Prune
June Fourth
Kaiser [not sure if they mean 'Kaiser Wilhelm' or something else, as there are many domestica plums with "Kaiser" in the name. -ASC]
Large English
Late Orange
Late Orleans
Late Tragedy
Leighton Italian
Liberty Prune
Long Green
Long Stem
Los Angeles
Miller Superb
Missouri Green Gage
Mount Royal
New Oregon Prune
Papagone Prune (P. I.40498)
Purple Gage
Reuter Early Italian
St. George
St. Jean
St. Martin
Sharpe Imperial
Silver Prune
Smith Orleans
Smith Late
Stark Green Gage
Steward Prune
Super Prune
Tardeva de Moleta
True Blue
Turkish Prune(synonym of Italian Prune)
$2000 Prune
Uncle Ben
Williamson Tragedy
Yellow Egg
Yellow Gage
Yellow Imperial
York State Prune
Zucheriva del Vesuvia

Prunus salicina:
Becky Smith
Best’s Hybrid
Blood Plum
Blue Gown
Botan [this is a synonym for so many plums, it is impossible to tell which one they are talking about here. -ASC]
Del Norte
Earliest of All
Extra Early Satsuma
Miss Edith
Purple Flesh
Red June
Santa Rosa
San Francisco
Tribble Early Beauty
Wright Early (P. I. 43180)
Wright Purple (P. I. 43181)

Prunus americana:
Admiral Schley
Golden Queen
New Ulm
Skuyu [do they mean 'Skuya'? -ASC]
Prunus americana var. mollis Torr. and Gray:

Prunus nigra:

Plumcots (so-called):
Francis I
Poe Royal Cot Plum

Prunus insititia:
Big Mackey
California Wild
Damson Free
Damson Majestic
French damson
King damson
St. Julien
White damson

Prunus munsoniana:
Early June
Freestone Goose
Late Goose
Poole Pride
Wildgoose Improved

Native plum:

Prunus hortulana:
Forest Garden
Golden Beauty
Prunus hortulana var. mineri Bailey:

Prunus bokhariensis:
P. I. 40224

Species unknown:
May Queen

Prunus cerasifera:
De Caradene [Is this a typo and they meant De Caradeuc? -ASC]
Early Cherry
Extra Early Cherry

Prunus angustifolia var. varians Wight and Hedr.:

Prunus orthosepala Koehne:
Prunus orthosepala
Prunus subcordata Benth.:
Prunus simonii:

Supposed parentageVariety
P. salicina X P. simoniiAlhambra
P. munsoniana X P. salicinaAmerica
P. salicina X ?Apple
P. cerasifera X P. salicinaBanana
P. salicina X P. simoniiBartlett
P. salicina X ?Beauty Junior
P. salicina X ?Bilona
P. salicina X P. americana X ?Biola
P. insititia X P. salicinaBlack Beauty
P. salicina X P. munsoniana?Bruce
P. salicina X P. americanaBursoto
P. salicina X P. simonii X ?Cazique
P. simonii X ?Chaleo
P. besseyi X P. americanaCheresoto
P. americana X P. salicinaChoice
P. salicina X P. simoniiClimax
P. salicina X ?Combination
P. insititia X P. domesticaConquest
P. americana X P. maritimaCrimson Beauty
P. salicina X P. americana X P. simoniiDiscovery
P. salicina X Chickasaw plumDonley
(P. munsoniana X P. salicina) X P. salicinaDuarte
P. salicina X P. simonii X ?El Dorado
P. salicina X P. americanaEliott
P. salicina X P. americanaEmerald
P. salicina? X P. domesticaEndicott
P. besseyi X native plumEpoch
P. besseyi X P. salicinaEtopa
P. salicina X P. munsonianaExcelsior
P. besseyi X P. salicinaEzapatan
P. salicina X ?First
P. salicina X P. americanaFlichinger
P. salicina X ?Formosa
P. salicina X ?Funk
P. salicina X P. americana X ?Gaviota
(P. munsoniana X P. salicina) X ?Gee Whiz Plumcot
P. americana X P. simonii X P. salicinaGigantic
P. maritima X P. simonii X P. americana X P. nigraGlow
P. salicina X P. munsonianaGolden
P. salicina X native plumGonzales
P. hortulanavar. mineri X P. americanaHammer
P. americana X P. simoniiHanska
P. salicina X ?Happiness
P. salicina X hybridHowe [for unknown reasons, this row was entered twice in the printed yearbook -ASC]
P. salicina X P. americanaHoyt
P. salicina X P. simonii X ?Inca
P. americana X P. salicinaInkpa
P. salicina X Chickasaw plumJewell Carpenter
P. munsoniana X P. salicinaJuicy
P. salicina X ?June Twenty-fourth
P. americana X P. simoniiKaga
P. americana X P. nigraKahinta
P. watsoni X P. americanaKiowa
P. simonii X P. salicina X P. cerasifera X P. munsonianaLa Crescent
P. salicina X P. americanaLoring Prize
P. salicina X ?Los Gatos
P. simonii X P. salicinaMammoth
P. cerasifera X ?Marianna
P. salicina X P. americanaMay Beauty
P. salicina X P. simoniiMaynard
P. salicina X P. cerasiferaMethley
P. munsoniana X ?Milton
(P. simonii X P. salicina X P. cerasifera X P. munsoniana) X native plumMinnesota 109
P. insititia X P. domesticaMiracle
P. salicina X P. americanaMonitor
P. salicina X P. americanaMound
P. salicina X Chickasaw plumMrs. Bruce
P. salicina X (P. munsoniana X P. salicina)?Munson
? X P. munsonianaNona
P. salicina X P. americanaOmaha
P. salicina X (P. munsoniana X P. salicina)Opata
P. americana X P. salicinaPatten’s XX
(P. salicina X P. simonii) X ?Phoebe
(P. salicina X P. simonii) X ?Prize
P. hortulana X P. americanaReagen
P. salicina X Chickasaw plumRed Ball
P. salicina X P. americanaRed Wing
P. hortulanavar. mineri X P. cerasusRoadside
Russian hybrid
P. salicina X ?Sacramento
P. besseyi X P. americanaSansoto
P. besseyi X P. salicinaSapa
P. simonii X P. salicina X P. cerasifera X P. munsonianaShiro
P. salicina X P. angustifolia var. variansSix Weeks
P. salicina X ?Solano
P. spinosa X P. domesticaP. I. 32671
P. spinosa X P. domesticaP. I. 32673
P. salicina X P. americanaStella
P. salicina X Chickasaw plumSweetheart
P. salicina X (P. salicina X P. simonii)Tanwick
P. salicina X P. munsonianaTerrell
P. americana X ?Theo. Williams
P. salicina X ?Thunder Cloud
P. americana X P. simoniiToka
P. simonii X P. americanaTokata
P. salicina X P. americanaTonka
P. simonii X P. salicina X P. cerasifera X P. munsonianaUnderwood
P. salicina X ?Upright
P. salicina X P. cerasiferaVesuvius
P. besseyi X P. salicinaWachampa
P. salicina X P. americanaWaneta
P. salicina X P. hortulanaWaugh
P. salicina X P. simoniiWickson
P. domestica X P. salicinaWilma
P. salicina X P. americanaWinona
P. salicina X ?Zulu

Prunus alleghaniensis
P. besseyi
P. davidiana
P. fremontii
P. mexicana

P. mira
ρ  This list of variety names is approximately as submitted by the California station. The names are those under which the material is recorded, and not all of them are necessarily intended as authentic variety names. The list apparently contains a considerable number of names representing local strains and other names that do not conform to the generally accepted code of nomenclature. It is impracticable to attempt to bring the nomenclature in all cases into harmony with the code, therefore only a few changes representing obvious differences have been made.

ψ Burbank’s achievements and limitations have also been summed up critically by Jones (22).