The cytokinin 6-benzyladenine (BA) and gibberellins A 4 + A 7 (GA 4+7 ), but not GA 3 , increased the fruit length-diam (L/D) ratio of ‘Delicious’ apples. Prominence of the points near the fruit calyx was increased more by BA than by GA 4+7 , but increased most when the 2 were combined. Sprays during bloom were more effective than either postbloom or prebloom sprays. A bloom spray combining GA 4+7 and BA at 100 ppm each decreased fruit set of open pollinated flowers in one year, but not in another. Concentration of 50 ppm or less altered fruit shape without any significant effect on the number of seed, fruit set, firmness, or fruit size.
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Stembridge et al. (1972) studied this question.