Control of postharvest decay in organic grown apples by hot water treatment

In general, organic grown apples (Malus x domestica Borkh.) are not treated with chemical fungicides to prevent storage decay and these fruits may suffer up to 30% decay during storage. Preliminary experiments had shown that hot water dipping of apples may be an alternative. To inhibit Gloeosporium rot (Pezicula alba, P. malicords) water temperature may be of about 50 degrees C and dipping time from 60 sec up to 180 sec. The present investigation was conducted to test different ranges of temperatures (49 degrees C, 51 degrees C, 53 degrees C) and dipping time periods (60 see, 120 sec, 180 sec) in 'Ingrid Marie' apple cultivar. The objective was to determinate the suitable hot water treatment that prevent decay incidence and maintain fruit quality (firmness, scale symptoms). Monifia fructigena was reduced up to 83% by the hot water treatment at 53 degrees C and 180 sec dipping time. With this treatment Gloeosporium rot was also reduced up to 92% but the incidence of decay with Nectria galligena increased in the 60 sec treatment at all temperatures. Scale symptoms were found when the fruits were treated at 51 degrees C and - 180 sec. There was no effect on fruit firmness after the heat treatment. For the reduction of post harvest decay, the treatment 53 degrees C and 180 sec is recommended. For cultivars with a high sensitivity to skin disorders it is recommended dips for 120 sec or 180 sec at the highest cultivar specific temperature showing no symptoms.