FRUIT - Tree Stocks Are Improving

The stocks which make the root system of budded and grafted trees have received more attention in recent years than formerly, although our knowledge of the underground part of such trees and the important, part it bears in the trees’ well-being is still far less than what we know of varieties and many other factors in fruit production. Evidence clearly indicates that some improvement in the performance of orchard trees may be had by better choice of stocks.

The interest of nurserymen, growers, and scientists has brought about a great deal of experimental work which is now beginning to yield results. Much time and energy must still be expended on such experiments, however, before the choice of the most suitable stocks can be made with the certainty of results now obtainable in the choice of the best adapted varieties.

At present a large proportion of the seed for the domestic production of fruit-tree stocks is imported. The seedlings themselves are also imported in large quantities. Aside from the danger of introducing insects and diseases, the behavior of imported seeds and seedlings has often proved unsatisfactory by reason of poor germination of the seeds or in variability of the seedlings. A search for domestic seed of good quality has shown that resources not hitherto utilized are already available for some of the important fruit stocks, while others can be produced without difficulty in a few years’ time by growing trees for the purpose.

For apple stocks, French crab seedlings have been most largely used for many years, Seed from some of the widely grown varieties of apples appear to possess superiority over French crab, according to experiments by the United States Department of Agriculture which have been under way for the past five years. Many of these varieties supply seed that germinates well and the resulting seedlings are vigorous and make good unions when budded or grafted. Seedlings of several varieties are hardier than French crab. Among them are McIntosh, Tolman Sweet, Oldenburg (Duchess), Rhode Island Greening, and Fameuse. Seedlings of other varieties which give evidence of desirability except in the northern sections, are Delicious, Winesap, and Stayman Winesap. Seeds of all these are available in large quantities from cider pomace in sections where the varieties are grown commercially.

Mazzard and Mahaleb, the two principal cherry stocks, are at present mainly imported from Europe.  Mazzard cherry seed from the roadside and pasture trees of Pennsylvania, Maryland, and Virginia within the past two or three years has been found superior to the imported seed. These wild trees are the descendants of the sweet cherries brought from Europe in colonial days. They have undergone vigorous selection under the severe conditions in which they grow in the wild. These wild trees occur over a wide range and are sufficiently productive to assure an ample supply of seed every year.

For Mahaleb cherry seedlings which are used in greater numbers than any other cherry stock, no adequate supply of seed is available in this country at present. Uncertain germination of imported seed has been one of the drawbacks to the production of seedlings in this country. On the other hand, seed from trees locally grown and handled to prevent severe drying during the interval between collecting and planting gives reliable germination. As Mahaleb trees come into bearing at an early age and are productive, no reason is apparent why a domestic supply of this species should not be grown for its seed.

A form of Morello cherry used in northern Illinois in a limited way for many years has recently received more attention on account of the excellent performance of the trees worked on it. It is a dwarfing stock propagated by suckers.

Myrobalan plum seedlings vary widely in their characteristics.  Improvement 1n the quality of this most widely used plum stock is being brought about by selecting forms that produce the most desirable type of seedlings and growing these selections in orchards for their seed. In California a considerable proportion of the Myrobalan seed annually needed for the entire country is already available, and the supply is increasing.

Experiments are also being directed to another promising means of improvement in fruit-tree stocks by eliminating the variability recognized in nearly all seedlings. Individuals are sought that have outstanding superiority in such qualities as affinity for the varieties to be worked on them, hardiness, adaptability to a wide range of conditions, and resistance to insects and diseases. These selected individuals are propagated by cuttings or layers rather than by seed, thus reproducing their characteristics with uniformity. Such means of obtaining stocks is a departure from established nursery practice in the United States, seedlings nearly always being used except for dwarf apple and pear stocks. It is not a new idea, however, for in Europe it is very widely used.

Besides the selection and proving of individuals, the problem of inexpensive and rapid propagation is an important one. Most types of fruit stocks do not root easily from stem cuttings. Root cuttings, however, make plants readily in some cases, while in others layers are better. Stocks thus propagated necessarily cost more than seedlings, but this added cost of a few cents per tree would be more than justified if a better tree could be had by their use. Several apple, cherry, and plum selections already made give promise of exceptional merit and are now being propagated for further tests before introducing them.

Of the plants used for the adornment of home surroundings, the Japanese flowering cherries are being more generally planted as they become known. These are most frequently worked on Mazzard as being the most readily available stock. The trees, however, have often proved short-lived. Several oriental species and forms more closely related to the varieties appear more suitable. Among those that show special promise are Prunus serrulata and its form, P. serrulata sachelinensis and seedlings of the variety Yoshino.

Several stocks for hybrid tea roses that give evidence of merit are being tested in comparison with the stocks generally used, which are manetti, Japanese multiflora, and others. One of these is a form of Rosa multiflora introduced from China by Chenault and received by the department from the Arnold Arboretum. Besides having the desirable qualities of the Japanese multiflora, this form is even more vigorous and has larger canes which root easily as hardened cuttings.  Plants grown from cuttings are more easily budded than the Japanese multiflora seedlings. Another promising rose stock is a form closely related to R. canina which has so far proved free from the tendency of that species to throw suckers from below the point of union.  R. odorata, S.P.I. 22449, while lacking in the extreme hardiness of the two stocks just mentioned, is proving to be a valuable stock for greenhouse forcing roses.