Delayed and prolonged ethylene treatment alleviates firmness asynchrony enhanced by 1-methylcyclopropene exposure in Guatemalan-West Indian avocado

Studies were conducted to determine the efficacy of a delayed and prolonged ethylene treatment in alleviating firmness asynchrony enhanced by 1-methylcyclopropene (1-MCP) exposure in avocado. 'Booth 7' and 'Booth 8' avocados, mid-season cultivars in Florida, were harvested and immersed in water (control) or aqueous 1-MCP at 16.7 mu mol L-1 a.i. (900 mu L-1) for 1 min at 20 degrees C; all fruit were held at 20 degrees C/89 +/- 2% relative humidity until ripe, based on whole fruit firmness, respiration and ethylene evolution. The effect of delayed and prolonged ethylene treatment was investigated by exposing 1-MCP-treated fruit to ethylene (100 mu L L-1) for 2 or 4d at 20 degrees C upon reaching two progressive ripening stages (120 N or 80 N of whole fruit firmness, respectively). Ripe fruit (10-15 N) from all treatments were assessed for peel color, pulp firmness and polygalacturonase (PG) activity. 1-MCP significantly delayed ripening of 'Booth 7' and 'Booth 8' avocado. Firmness asynchrony was confirmed in control fruit of both cultivars, with a difference of more than 20% in pulp firmness between apical and distal end segments regardless of ripeness stage.1-MCP-treated fruit showed pronounced firmness asynchrony, with pulp firmness for apical end 10-fold higher than for distal end. PG activity was not directly related to firmness asynchrony, since even when strong asynchrony was observed for 1-MCP-treated fruit, PG activity did not differ from control. A 2-d delayed exposure of fruit at either 120 N or 80 N whole fruit firmness to ethylene was not consistently sufficient to promote ripening recovery (in terms of whole fruit firmness). However, a prolonged, 4-d ethylene treatment of fruit at either progressive ripening stages from both 'Booth 7' and 'Booth 8' effectively overcame the pronounced firmness asynchrony caused by 1-MCP treatment. (C) 2015 Elsevier B.V. All rights reserved.