Vegetative Formations

Vegetative formations of fruit trees are represented by various types of shoots and branches, whose main purpose is to increase the size (volume) of the crown and replenish it with new, more vigorous branches in place of aging ones.

Shoots are growths of the stem and its branches until they are covered with leaves. After leaf fall, they are called branches. By growth strength and morphological features, shoots are divided into elongated (auxiblasts), which have strong growth, clearly defined internodes, well-formed lateral buds, and shortened (brachiblasts), whose length does not exceed several centimeters, and internodes are so short that it is often difficult to distinguish them.

By their position in space, shoots are divided into vertical (orthotropic) and horizontal (plagiotropic) shoots. By type of buds — vegetative, in which all buds are growth buds, and generative, whose apical bud, and sometimes part of lateral buds, are flower buds.

Fig. 19. Shoot (a) and one-year branch (b).

but branch out at a sharp angle and grow as strongly, if not stronger, than the continuation shoot, i.e., they compete with it for the leading position on the branch.

Some buds may sprout in the same year they form, when the second half of summer and early autumn are warm and moist. Such shoots are called premature, summer, or Ivanov shoots. The formation of summer shoots from early buds is common in stone fruits.

Whorls (whorl, fatty, or water shoots) — strong vertically growing shoots, usually arising on multi-year branches from reserve or adventitious buds. On whorls, buds are sparsely arranged, internodes are much longer than on ordinary vegetative shoots, leaves are large. Whorls appear at the base of large branches after heavy pruning, at the apex of a curved branch, and also after frost damage. The ability to form whorls depends on the variety: trees of some varieties form a large number of whorls, others — very few.

Regenerative shoots appear as a result of disruption of the correlation between the above-ground and underground systems, primarily at the sites of pruning or branch breakage. They form from dormant and adventitious buds. Their growth begins and ends later than normal (spring) shoots. This group also includes adventitious shoots, which form from additional buds located on the side of the main branch, from embryonic formations present in annual rings, at sites of injury, and on roots.

Shoots arising from mixed buds, together with generative organs, are called replacement shoots.

Shoots arising from roots are called root-sprouts. On the underground part of such branches, adventitious roots form. Considering that fruit trees are typically composed of a scion and rootstock, and that wild sprouts arise from the rootstock, root-sprouts should be removed, otherwise they may "smother" the tree. Moreover, the growth of such shoots consumes a great deal of assimilates, water, and mineral nutrients.

A special group are thickening shoots. These include all shoots forming on one- to two-year-old plants in the zone of the future trunk of the tree. The name is traditional: in old nurseries, such shoots were left to grow throughout the summer to achieve maximum trunk thickening.

The length of a shoot — an important indicator of the activity of physiological processes, the condition of the tree, and the effectiveness of applied agronomic practices — is closely linked to the prospects of fruiting. Almost complete cessation of shoot growth indicates that,

Fig. 21. Whorls: a — on an old branch; b — on a horizontal branch; c — after heavy pruning; d — on the apex of a curve; e — at a site of severe injury; f — below the frost damage site.

fruit production will soon sharply decrease, especially fruit quality. For reference, it should be known that strong shoots are those exceeding 60 cm in length for young trees and more than 40 cm for fruiting plants; moderate — respectively 50 cm and 30 cm; weak — less than 40 cm and 20 cm. Further reduction in annual branch growth in length necessitates urgent measures to restore growth.

Fig 22. Shoots: a — replacement on fruiting spurs; b — regenerative; c — root-sprouts.