APPLE TREE CANOPY DEVELOPMENT AND PHOTOSYNTHESIS AS AFFECTED BY ROOTSTOCK

Trees of apple (Malus domestica Borkh.) with 'Starkspur Supreme Delicious' as the scion grafted on nine different root-stocks (Ottawa 3, M.7 EMLA, M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC-9, MAC-24, OAR 1) were studied in their 8th and 9th years. Canopy seasonal development and its light interception followed by fisheye (hemispherical) photography showed that rootstock affected the amount of structural wood, the rate of canopy development, and final leaf area. However, rootstock did not affect the sigmoidal pattern of canopy development. Light interception was linearly correlated with tree dimensions and yield. Leaf net photosynthesis (P(n)) of trees on dwarfing rootstocks tended to be lower than P(n) rates of trees on more vigorous rootstocks. Rootstock did not affect the scion P(n) response to different illumination levels. Shoot leaves, spur leaves on spurs without fruit (S - F), and spur leaves on spurs with fruit (S + F) from trees on M.26 EMLA and OAR 1 showed no differences in P(n) rates. However, for both rootstocks, shoot leaves had the highest P(n) rate, S + F the lowest, and S - F leaves had intermediate values.