ON THE ROLE OF ETHYLENE IN APPLE FRUIT SET

To determine if ethylene production by apple flowers limits fruit set, aqueous sprays of aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, and of (2-chloroethyl) phosphonic acid (ethephon), an ethylene-generating compound, were applied to branch units of trees of 3 apple cultivars (McIntosh, Red Prince Delicious, and Golden Delicious) at full bloom. Fruit set was recorded at intervals from 3 weeks after full bloom until harvest, and samples of flower and fruit clusters were removed at intervals of 1 to 10 days after treatment for measurement of ethylene evolution. The clusters were held with their bases in water in sealed containers in the dark at 21° C, and CO₂ was absorbed by placing a filter paper wick moistened with 40% KOH in each container. The jars were ventilated after 4 hr, and ethylene production was measured during the subsequent 4 hr by gas chromatographic analysis of 1 m1 samples of air from the chambers.