Stern, R.A., MIGAL, Galilee Technology Center, P.O. Box 831, Kiryat Shmona 11016, Israel
Flaishman, M.A., Department of Fruit Trees, Institute of Horticulture, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

The final fruit size of apple depends on the number of cells present at fruit set, the subsequent number of cell divisions and the extent to which these cells expand. However, cell division during the early stage of fruit development has a major influence on final fruit size. Studies with synthetic cytokinins CPPU and BA have shown promising results in increasing fruit growth of grape, kiwifruit, persimmon and pear, but in apple the fruit becomes malformed. In Israel, the summer is very hot and dry. Therefore the duration of the stage of cell division stage is short, and consequently small fruits develop, especially 'Royal Gala' apple. During three consecutive years (1999-2001) we found that the application of CPPU at a concentration of 10 mg.L-1, or BA at a concentration of 50 mg.L-1, two weeks after full bloom, increased the fruit size. The yield of harvested fruit ≥75 mm increased by more than 50% with no effect on fruit drop, fruit shape and seed number. Our findings demonstrate the effectiveness of CPPU and BA on increasing the size of 'Royal Gala' apple. Preliminary results on 'Red Delicious' apple show that these cytokinins may be used for other apple varieties as well.