Apical control of lateral bud development and shoot growth in mulberry (Morus alba)

Abstract

Measurements of changes in the degree of dominance by upper laterals over lower ones in coppice shoots (1‐year‐old stems) of 12‐year old low‐ pruned stumps of mulberry (Morus alba L. cv. Shin‐ichinose) were made by removal of upper stem sections (pruning) or of lateral buds (debudding.) before spring bud burst, as part of a study of the factors involved in dominance relationships between the developing buds and elongating shoots. Besides inhibition of lower laterals by the upper, leading shoots, there was evidence for mutual inhibition (competition) of neighboring laterals along the stem. Thus in stems in which every other bud, or 4 out of every 5 buds were removed, there was a delay in growth cessation of lower laterals and their greater elongation than in controls. Such competition was seen to exist even between the uppermost and sub‐terminal laterals, since the former elongated more in the absence of the latter.In contrast to high and middle pruned stems, the delay in sprouting of the buds in low‐pruned stems resulted in limited elongation of the shoots from such buds. This inhibition was removed when all the stems on a stump were pruned to the same length, suggesting that it was associated with intact stems with actively growing laterals. Patterns of regrowth of the short shoots (lower laterals) after summer pruning (middle‐pruned) depended on the extent of removal of other stems with vigorously growing, upper laterals. These results demonstrate that both acropetal and basipetal influences are important in bud and shoot dominance relationships.