Postharvest decay control of citrus fruit by preharvest pyrimethanil spray

Preharvest infections or conidia load on fruit surface by Penicillium digitatum, P. italicum, Alternaria citri and other filamentous fungi can cause important postharvest losses of citrus fruit. Reduction in pruning frequency occurred in the last decade together with un-picked yield that eventually rots on the trees have increased the risk of postharvest decay especially when environmental conditions at picking time are favourable to pathogens' development. Sanitation procedures in the packinghouses, alternate use of postharvest fungicides with different modes of action, along with fungicide application before harvest could be an effective approach to minimize postharvest decay in citrus fruit. The present study investigated the effectiveness of a preharvest treatment with pyrimethanil (PYR), a broad spectrum fungicide, recently registered in different citrus-producing countries for postharvest treatments of citrus fruit and widely used worldwide as a preharvest treatment to control various diseases in different crops. PYR (750 mg/L) was sprayed by a hand-back sprayer at run-off on 'Fremont' mandarins. The day after the treatment, half of the trees were sprayed with a 10(4) conidial suspension of P. digitatum at run-off. Fruit were harvested following 2 or 4 weeks from treatments. Sound or either wounded 2-mm-deep and 2-mm-wide or superficial wound-scratched fruit were stored at 20 degrees C and 90% RH and inspected for decay after 1, 2 or 3 weeks of storage. In fruit harvested after 2 weeks from field treatment, PYR remarkably reduced decay development during two weeks of storage in sound fruit and in wound-scratched fruit and was fairly effective even after 4 weeks from treatment, but was ineffective in fruit wounded 2 mm deep and 2 mm wide. PYR was also effective in reducing preharvest decay incited by P. digitatum, P. italicum and Botrytis cinerea, but not by other pathogens. Results show that preharvest treatment with PYR could be a feasible approach to reduce postharvest chemical control of decay of citrus fruit.