The role of ethylene in fruit and petal abscission in the red raspberry (Rubus idaeus L. cv. Glen Clova)

Abstract

Weakening of fruit and petal abscission zones in Rubus idaeus L. cv. Glen Clova was accompanied by increased rates of ethylene production. Both processes were accelerated by a supply of exogenous ethylene. In the ripe fruit natural ethylene levels were saturating. The rise in ethylene production clearly preceded petal abscission but in fruit the increase virtually coincided with the start of weakening. Raspberry fruit of other varieties and blackberries clearly showed the abscission zone weakening could precede any increase in ethylene production.

The internal ethylene concentrations of Glen Clova fruit at the mottled stage reached those levels which had to be added to stimulate abscission (ie 0.25 to 0.5 ppm). This is the very stage at which abscission zone weakening was first noticeable.

Both fruit and petal abscission was retarded by the application of inhibitors of ethylene production ( AVG, Co 2+) or action (Ag+ ). Likewise a reduction in the internal ethylene under hypobaric pressure also retarded fruit abscission. None of these treatments were totally capable of preventing abscission.

In fruit abscission the receptacle appears to have an important role. The increase in receptacle ethylene production precedes that of the drupelets. The enlargement and swelling of the receptacle tissues are important in both abscission zone weakening and ethylene production. This receptacle development may in turn be controlled by the development of fertilised drupelets.

The ethylene production in both fruit and petal abscission is limited initially by the supply of ACC. In both cases endogenous ACC levels increase in step with ethylene production.

Ethylene's role as a coordinating/accelerating agent in fruit and petal abscission is discussed.