In order to study the effect of gibberellin (GA_(4+7),) with or without benzyladenine (BA) treatments on the fruit development of apple, this experiment was carried out in 6-year old ´Orei´, ´Starkrimson´, ´Jonathan´, and ´Fuji´ cultivars grafted on M26 rootstock plant. Lanolin paste of GA_(4+7) and BA was applied to the fruit stalks on May 21 and 31, 1978. Rapid fruit development occurred 10 days after the treatment regardless of the cultivars. No difference in fruit diameter and weight was observed between the GA_(4+7), 1,500ppm with and without BA 600ppm treatment. 3,000ppm of GA_(4+7) treatment was the most effective in ´Orei´ and ´Fuji´ cultivars, but no difference between 1,500ppm and 3,000ppm in ´Starkrimson´ cultivar.
Although the initial development in fruits treated with GA_(4+7) was very rapid, the difference of fruit size at harvest was not great compared with the early stage of fruit development. Fruit weight when harvested was increased by 12∼20%, 0∼16%, and 3∼11% by GA_(4+7) 3,000 ppm, GA_(4+7) 1,500ppm and GA_(4+7) 1,500ppm+BA 600ppm treatments, respectively. As a result, GA_(4+7) treatment increased greatly the ratio of large fruits in all cultivars.
Fruit firmness tended to decrease by GA_(4+7), treatment, and soluble solids and acidity of fruit were not influenced greatly by treatments.
Lanolin paste treatment of GA_(4+7) to the fruit stalks tended to induce fruit skin russet symptom.
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