THE PROPAGATION AND IDENTIFICATION OF 

 CLONAL ROOTSTOCKS FOR THE APPLE 



By J. K. Shaw, Research Professor of Pomology 



There is now considerable interest in semi-dwarf and dwarf apple trees for the 

 orchard and home garden. Such trees are produced by budding on certain clonal 

 rootstocks. These rootstocks must be grown by cuttings or layers and are not 

 available in sufficient numbers at the present time. Therefore, a discussion of 

 their characteristics and methods of propagating them may be helpful. 



Apple trees become dwarfed chiefly because of precocious fruiting. When 

 much of the synthesized material from the leaves is used to produce apples, there 

 is that much less for vegetative growth. This is the condition in mature bearing 

 trees. 



Dwarf trees commence production and mature earlier than trees on "standard" 

 or "free" stocks. They form fruit buds at an earlier age because of some influence 

 of the rootstock. It is not known just what this influence is, but some sugges- 

 tions may be advanced. Fruit buds are formed in June and July. It is known 

 that a restricted water supply and an accumulation of starch in the tree precede 

 or accompany fruit bud differentiation. It has been shown that dwarfing root- 

 stocks cease root growth earlier and that this lowers water absorption, also that 

 the graft union restricts the passage of water, and that a greater accumulation 

 of starch takes place in dwarf trees. It may reasonably be assumed that re- 

 stricted water supply (and possibly nitrogen and other mineral matter) together 

 with an accumulation of starch and possibly some other substance or substances 

 are effective in forming fruit buds. And it is certain that fruit production is 

 very effective in reducing rate of growth. 



THE PROPAGATION OF APPLES 

 Seedling Rootstocks 



The usual method of propagating apple trees is by budding or grafting the 

 desired variety on seedling rootstocks. Seeds are obtained from various sources 

 such as cider mills and canning factories. After a period of exposure to low 

 temperatures under moist conditions, the seeds will germinate, and after one 

 season of growth, the seedlings are transplanted and budded to the varieties 

 desired, or the seedling roots may be whip grafted and set in the nursery. After 

 one or more seasons of growth in the nursery, the trees are ready for planting 

 in the orchard. Apple seedlings are extremely variable in vigor and growth 

 habits, and it seems reasonable to expect trees budded or grafted on them to 

 differ greatly in vigor and production. As a matter of fact, such trees are rather 

 remarkably uniform insofar as stock effect is concerned. Most of the differences 

 seen in the orchard are due to soil conditions, though injuries of various kinds 

 sometimes result in inferior trees. 



Seedling-rooted trees seem to be more variable in England and on the Conti- 

 nent than they are in America. Probably both seedlings and nursery trees are 

 more rigidly graded here, thus eliminating weak trees before they are planted in 

 the orchard. Climatic conditions here and in Europe differ and may cause 

 differences in the variability of orchard trees. Trees on clonal rootstocks are 

 much in favor in England largely because they are more uniform. The American 



