Role of Ethylene in Avocado Fruit Development and Ripening

A survey of avocado ( Persea americana Mill.) fruit drop and ethylene 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. Fruitlets weighing up to 0-2 g dropped at a rate of over 30 per cent per week. With larger fruits, the rate was under 1 per cent per week. Fruit drop ceased after September, when fruit growth declined and the seed coat began to shrivel. A positive correlation was found between the rate of fruitlet and fruit drop and ethylene production. Fruitlets with defective seeds produced ethylene at a very high rate of 7-10 times more than apparently normal fruits. The high incidence of defective seeds might be the cause of the very high levels of ethylene production by young avocado fruitlets. The seed was found to be the main site of ethylene production in fruitlets. Abscisic acid (ABA) levels in young abscissing fruits were 7 times as high as those in non abscissing fruits.