Date of Award
Master of Science
Joe S. Alexander, Roger B. Thompson, Gordon E. Hunt
Pruning is one of the oldest and most universally practiced orchard operations. (1) The fundamental objectives of pruning are to improve the quality and quantity of fruit and to lower the cost of production. There is no horticultural practice on which there is greater diversity of opinion or application of procedure. (7) The average grower, when asked why he does or does not prune, generally will reply that it is good or not good for the tree. (?) Some of the specific objectives assigned to pruning are (1) to open the tree for more fruit color, (2) train to a desired form, (3) remove dead and diseased parts, (4) remove water sprouts and cross-branches and (5) to thin fruit. (7) Pruning may vary in three respects; (1) the amount of wood removed, or severity, (2) the kind or position and (3) the season. There are two methods of pruning; "thinning out" and "heading back." "Thinning out" is a method that removes whole shoots or branches. "Heading back" removes a portion of a shoot. The lateral buds of most species of plants are formed in the axil of each leaf. They seldom grow immediately, but tend to remain dormant during the season in which they are formed. Failure of the newly formed lateral buds to grow immediately is commonly attributed to "apical dominance." If the terminal bud is removed, one or more of the lateral bids may begin to grow. Inhibition of the lateral buds by the terminal bud seems to be a polar phenomenon influenced by gravity. It has been shown, using indoleacetic acid on the cut surface following removal of the terminal bud, that the lateral buds remain quiescent as if the terminal bud were present. This suggests that an auxin might be produced by the terminal bud or in the region of the terminal bud. It is interesting to speculate on the reasons why the terminal bud, which is considered as the site of auxin production, continues to grow actively when buds behind it are inhibited. Apple flowers are usually borne terminally on short shoots known as spurs. Occasionally flowers are borne terminally on shoots. Some varieties produce flowers rather commonly in this fashion. Individual spurs seldom bear annually, although the spurs of some varieties are more likely to do so than others. Heavy annual production depends on the formation of numerous new spurs and the maintenance of old spurs in a vigorous condition. Spurs are usually produced from lateral buds of the preceding season's growth, rarely on old wood from either latent or adventitious buds. Previous studies have been done to determine the effect of severity of pruning on trees as a whole, but not on the effect of bud performance on shoots. The objectives of this investigation were to determine the effect of heading back one-year-old wood on the establishment of the spur system, the production of new shoots, and the forcing of buds which are expected to remain dormant or latent.
Baird, Douglas D., "The influence of heading back on bud performance of one year-old apple shoots. " Master's Thesis, University of Tennessee, 1963.