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

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.