Role of Ethylene in Avocado Fruit Development and Ripening: I. FRUIT DROP

A survey of avocado (Persea americana Mill.) fruit drop andethylene production was carried out during fruit development.Natural drop of avocado fruitlets started soon after set (May)and continued at a gradually decreasing rate until September,except for a temporarily increasing rate in late July. Fruitletsweighing up to 0?2 g dropped at a rate of over 30 percent perweek. With larger fruits, the rate was under 1 percent per week.Fruit drop ceased after September, when fruit growth declinedand the seed coat began to shrivel. A positive correlation was found between the rate of fruitletand fruit drop and ethylene production. Fruitlets with defectiveseeds produced ethylene at a very high rate of 7–10 timesmore than apparently normal fruits. The high incidence of defectiveseeds might be the cause of the very high levels of ethyleneproduction by young avocado fruitlets. The seed was found to be the main site of ethylene productionin fruitlets. Abscisic acid (ABA) levels in young abscissing fruits were 7times as high as those in non-abscissing fruits.