Effect of 6-benzyladenine application time on apple thinning of cv. 'Golden Delicious' and cv. 'Idared'

Abstract

Apple thinning of cv. 'Golden Delicious' and cv. 'Idared' was studied after the application of 6-benzyladenine (BA) 100 mgl-1 and 50 mgl-1 respectively, applied at different time of blooming period and over a wider range of fruitlet diameter. When BA 100 mgl-1 was applied on cv. 'Golden Delicious', significant reduction in final fruit number per tree was observed if applied at the end of blooming period or when fruitlet diameters were 6 mm, 15 mm or 20 mm, but thinning was not significant if applied at full bloom or at 10 mm or 25 mm fruitlet diameter. The share of bigger fruits of cv. 'Golden Delicious' (> 65mm) was increased at all BA application time treatments, but significantly only in the treatment of hand thinned trees. Regarding the BA applications carried out on cv. 'Idared', significant thinning response was noticed in the case of BA sprayed at the end of bloom and at 10 mm of fruit diameter. The mean fruit weight of cv. 'Idared' apples was increased significantly only if BA was applied at 10 mm fruitlet diameter. Although the thinning results were inconsistent for two studied cultivars it was demonstrated from the trial that BA could be active as a thinner if applied over a wider phenological interval, at the end of blooming period up to 20 mm fruitlet diameter.