INFLUENCES OF UNICONAZOLE ON GROWTH, FRUITING, AND PHOTOSYNTHETIC ACTIVITY OF TISSUE CULTURE-PROPAGATED OWN-ROOTED APPLE-TREES

Tissue culture-propagated (TC) own-rooted 'Gala' and 'Triple Red Delicious' apple trees grown at three planting densities were not treated (TC control) or were treated with annual uniconazole sprays or two trunk drenches starting with the third or fourth growing season. Budded (BUD) trees on M.7a rootstock were also included as controls. After both the fifth and sixth growing seasons, the cultivars grown and the treatments applied had more influence on the attributes measured than did planting densities. Flowering and yield were greater on 'Gala' trees compared with 'Triple Red' for the fifth, but not the sixth season. The tree propagation method did not influence flower numbers and yield of 'Gala' trees in either the fifth or the sixth growing season but flower numbers were greater on BUD compared with TC trees of 'Triple Red' for both seasons. Flowering of TC 'Triple Red' trees tended to be increased by uniconazole treatment. Uniconazole applied by the trunk drench method markedly retarded vegetative growth of 'Gala' trees during the fifth season but flowering was reduced the following season. The trunk cross-sectional area of control TC trees for both cultivars increased more than for BUD trees but uniconazole treatment slowed trunk cross-sectional area increase so that treated TC trees were maintained at nearly the same size as BUD trees. Overall, 'Triple Red' leaves had higher chlorophyll concentrations than 'Gala' leaves, but there were no differences between BUD and TC leaves for net photosynthetic rate (Pn), stomatal conductance for water (g(sw)), relative chlorophyll concentration, or specific leaf weight (SLW). Uniconazole treatment increased mean seasonal Pn, g(sw), relative chlorophyll, and SLW compared with controls.