Boron and fruit quality of apple

Abstract

A field experiment was conducted in Yunnan, P. R. China to examine effects of boron (B) fertilizer on fruit yield and quality of apple (Malus domestica cv. Golden Delicious). Four rates of borax (0, 40,80, 160 g tree-I) were applied to the soil at full bloom, with 4 replicated trees in each treatment. A survey of commercial apple orchards was also conducted to establish the relationship between fruit B concentration and quality. In the field experiment, increasing rates of B application, increased fruit B concentration but decreased the rate of fruit drop by the end of the second wave of fruit drop in June. Fruit began to drop when fruit B concentrations were about 12 and 8 mg B kg-I dry wt at the pea-size (1.5 cm fruit diameter) and June drop (3.5 cm fruit diameter), respectively. In both the field experiment and the survey, increasing fruit B concentration was correlated with increased fruit size and number of seeds, decreased firmness and titratable acidity, but unrelated to vitamin C concentration. It can be concluded that low B in the fruit is one of the factors involved in fruit drop. Optimal fruit quality was obtained when fruit B contained 14.7 mg B kg-1 dry wt corresponding with an application of 80 g borax tree-I. It is suggested that B may affect fruit quality through its influence on seed production.