Further studies were conducted from 1972 to 1973 to improve the measure in inducing parthenocarpy of Muscat Bailey A grapes with gibberellic acid(GA).
When the prebloom GA application was made at one time 14 days or 17 days before full bloom, 200 ppm was more effective concentration than 100 ppm for getting stably high seedlessness ratio. The repeated prebloom GA applications at 200 and 100 ppm or 100 and 200 ppm in the order 14 days and again 7 days before full bloom resulted in siginficantly higher seedlessness ratio as compared with the one time application at 100 ppm 14 days before full bloom.
The addition of benzyl adenine(BA) at 100 or 200 ppm to the GA solutions significantly raised the seedlessness ratio and improved the compactness of bunch resulting from the depressed elongation of peduncle and rachis and the increased berry set. These effects of BA were more prominent in proportion to the concentrations.
The appearance of the abnormal tissue like a pit developed at the core, which was reported in the previous paper, was not significantly affected by the repeated applications and concentrations of GA and also by the combined applications of BA with GA even though the rate of berries having such abnomal tissue fractuated from 2.4 to 17.9% depending on the years and treatments.