LONG-TERM EFFECTS OF PLANT GROWTH REGULATORS ON TISSUE-CULTURED APPLE TREES

Abstract

Tissue-cultured (TC) own-rooted `Gala' and `Triple Red Delicious' apple (Malus domestica Borkh.) trees, planted at three different spacings (1121, 747 and 561 trees per hectare) and treated with the plant growth regulators alar plus ethrel, paclobutrazol or uniconazole using several application techniques, were evaluated for a total of 9 years in the orchard. Cumulative yields did not differ between TC and budded (on M.7a) controls, although the budded trees had larger yields for the first 2 (`Gala') or 3 (`Triple Red Delicious') years of the 7 seasons in which fruit were harvested; yields from trees treated with alar-ethrel were significantly larger than for budded controls but did not differ from the TC controls. Uniconazole spray applications had an earlier and more consistent effect on fruit yield than any other uniconazole or paclobutrazol treatment, although cumulative yields were not as great as for alar-ethrel treated or TC control trees, but were equal to the budded control trees. The alar-ethrel combination had less effect on tree size control than most of the paclobutrazol and uniconazole treatments. Trees of `Gala' bloomed and fruited earlier than those of `Triple Red Delicious' and had significantly higher yields.