Rooted stool-bed layers of Malling Merton (MM) 111 apple trees were container-grown in a greenhouse and trained to a single shoot. When shoot length averaged 73 cm, the following treatments were applied: a) check, untreated (CK); b) tipped (shoot apex removed) and top 1/2 of shoot disbudded (T-DB); c) top 1/2 of shoot disbudded and defoliated (UT-DB-DF); d) tipped, and top 1/2 of shoot disbudded and defoliated (T-DB-DF); e) pruned at mid-shoot (P); or f) pruned at mid-shoot and disbudded (P-DB). Treatments UT-DB-DF, T-DB-DF, P, and P-DB delayed the eventual decline in net photosynthesis (Pn) and total chlorophyll content exhibited by the check. The delay in the decline of Pn and total chlorophyll content was maintained for the longest period in the UT-DB-DF, T-DB-DF, and P-DB treatments. Maintenance of Pn and chlorophyll levels following pruning or defoliation appears to result from an increased root : shoot ratio at treatment rather than an increased demand for photosynthates by subsequent growth. Treatment responses of Pn and total chlorophyll content were similar so that Pn per unit chlorophyll showed no treatment differences. Removal of leaves by either pruning or defoliation reduced total dry weight of the tree whereas tipping had no effect. Final dry weights of the basal stem, roots, and shank were reduced by pruning or defoliation. Lateral shoot growth induced by pruning caused an initial decrease in the shank diameter and root and shank dry weights of potted apple trees. / Master of Science

M.S.