Opposing effects of daminozide and ethylene on the induction of flesh softening in apple fruits

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Abstract
Summary Apple trees were sprayed in late July with daminozide in four seasons to suppress ethylene production and softening of harvested fruit stored in 2% O2, 2 at 3.5°C. In two out of three years daminozide applied at 0.43 g l−1 was ineffective whereas ethylene production, softening and the rise of soluble pectin were inhibited by 0.85 or 1.7 g l−1. In the third season all the spray treatments were ineffective. In bulk storage experiments a combination of daminozide treatment and ethylene removal by potassium permanganate-impregnated vermiculite led to the retention of fruit firmness in two years out of three; untreated fruit and fruit which received only one of the treatments softened to a similar extent. The dual treatment also inhibited the solubilization of pectin and the synthesis of butyl and hexyl acetates during ripening after storage. Whereas daminozide-treated fruit had higher chlorophyll levels than untreated fruit, ethylene removal had no effect on chlorophyll loss. A taste panel distinguished the low ethylene-daminozide treated fruit as firmer and less mealy than other treatments. However, this fruit had a higher incidence of storage disorders.