The Effects of Different Ratios and Concentrations of Benzyladenin and GA4+7 on Fruit Size and Yield of Apple Trees

Abstract

In 1996, benzyladenine, or GA4+7, or different ratios of BA: GA4+7 (100:1, 10:1 and 1:1) were applied to 10-year-old `Empire' apple trees on M.9 at 10-mm fruit size and 19-year-old `Redchief Delicious' apple trees on M.9 or M.9/MM.111 at 7.6-mm fruit size. Each chemical or combination of BA and GA was applied at three rates (50, 100, or 150 ppm) and at 75 ppm with 1.25 ml of carbaryl/L. At harvest, fruits were sampled from each treatment to determine fruit shape, firmness, color, total cell number, average cell size, and percentage of intercellular space. The positive rate response on fruit size and negative rate response on crop load of `Empire' became less significant for each formulation as the amount of GA4+7 in the formulation increased. The same was true for `Delicious', but less pronounced. At low rates of BA, formulations containing GA resulted in more thinning than BA alone. However, at higher rates of BA, formulations containing GA caused significantly less thinning than BA alone. For treatments combined with carbaryl, crop load increased linearly in `Empire' with increasing amounts of GA4+7 in the formulation. The treatment that provided the largest fruit size for `Empire' was BA@150 ppm, while for `Delicious' it was BA@75 ppm + carbaryl. Both varieties showed the greatest reduction in crop load with the 100:1@75 ppm+ carbaryl treatment when compared to the controls. These data suggest that GA4+7 in formulation with BA may inhibit the thinning action of BA at moderate and high rates.