Effects of Sugar and GA Contents on Flower Bud Formation of Bourse Shoots in Apple

Abstract

To investigate the relationship between sugar concentration, gibberellin levels and flower bud formation of terminal buds of bourse shoots in two apple (Malus domestica Borkh.) cultivars ‘Fuji’ and ‘Megumi’, different bearing levels, seeded and seedless treatments were performed. The flowering rate of terminal buds of bourse shoots bearing seeded fruits was lower than those of non-bearing and seedless fruit trees. In the fresh weight of terminal buds of bourse shoots, all treatments were the same in the beginning of June, and weights of buds from seedless trees were heavier than those of seeded fruit trees in the beginning of July. Assimilate of photosynthate produced by bourse leaves distributed to the terminal buds was affected by fruits rather than seeds, and it decreased as the dry weight of fruits per bourse increased. However, sugar concentrations of terminal buds of bourse shoots in the beginning of June also decreased as they bore more fruits. Decreased sugars of terminal buds were sorbitol and glucose, whereas sucrose was invariable. GA level of non-bearing and one type of seedless fruit tree were lower than three or one seeded fruit per bourse in the beginning of June, and it increased with the presence of seeds rather than with the presence of bearing fruit.