COULD ETHYLENE METABOLISM IN LEMON FRUIT INFLUENCE PETECA INCIDENCE?

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Peteca of lemon is a postharvest physiological disorder resulting in the collapse of the oil glands. Subsequently, the oil leaks into the adjacent tissue and causes a darkened depression. The occurrence can be severe, without any specific pre- or postharvest practises to employ to reduce the incidence. Over several seasons the incidence of peteca was investigated to identify factors that influence the incidence of the disorder. The first observation was the highly erratic incidence between seasons as well as within an orchard in a season, with the early fruits being highly susceptible. In experiments to identify postharvest factors which influence the peteca incidence, 3 ppm ethylene and 5% CO2 were applied in a continuous flow-through system (20°C for 3 d). The CO2 treatment resulted in significantly higher incidence compared to the rest. Following on from these results, postharvest Ethephon (2-Chloroethyl phosphonic acid) (200 and 400 mg/L) and AVG (aminoethoxy-vinylglycine) (400 and 800 mg/L) applications to fruit resulted in a significant reduction in peteca. In the subsequent season, the same treatments were applied in an orchard one week before harvest and a similar reduction in peteca was recorded. Ethylene production from these fruits after harvest was measured and showed a transient spike in fruits from the Ethephon treatment. The results collected could indicate a protective action of ethylene in reducing rind sensitivity to peteca. It is hypothesised that if the internal ethylene synthesis is increased prior to harvest in sensitive fruit, i.e. immature fruit, a reduction in peteca can occur.