Canopy Development, Photosynthesis, and Vegetative Growth as Affected by Apple Rootstocks

Abstract

Fisheye photographs were taken in 1988 from bud break to terminal bud formation under the canopies of ‘Starkspur Supreme Delicious’ apple trees on nine rootstocks in the 1980 NC-140 cooperative planting in Simcoe, Ontario. Each photograph was computer-analyzed for the percentage of sky cover. Rootstock affected the amount of structural wood, the rate of canopy development and the final leaf area. However, rootstock did not affect the pattern of canopy development. Photosynthesis (Pn) was measured under field conditions using a LI-COR 6200 portable photosynthesis system. Net Pn rates of trees on dwarfing rootstocks tended to be lower than Pn rates of trees on more vigorous rootstocks. Shoot leaves, spur leaves on spurs without fruit (S-F), and spur leaves on spurs with fruit (S+F) from trees on on M.26 EMLA and OAR 1 rootstocks showed no differences in Pn rates due to rootstock. However, for both rootstocks, shoot leaves had the highest, S+F the lowest, and S-F leaves intermediate Pn rates. Growth and yield components were assessed in 1987 and 1988, by harvest and defoliation of sample branches. Leaves were separated into shoot and spur leaves when harvested. Rootstocks strongly affected the number, area, and dry weight of shoot and spur leaves as well as the distribution between leaf types in both years. Rootstocks affected the number of spurs per cm limb circumference. Spur-leaf characteristics were correlated with yield efficiency while shoot-leaf characteristics were correlated with tree vigor.