Effects of preharvest oligochitosan sprays on postharvest fungal diseases, storage quality, and defense responses in jujube (Zizyphus jujuba Mill. cv. Dongzao) fruit

In order to evaluate effects of preharvest foliar oligochitosan (OCH) sprays on postharvest diseases in Chinese jujube (Zizyphus jujuba Mill. cv. Dongzao) fruit caused by Monillinia fructicola (G. Winter) Honey and Alternaria alternata (Fr.) Keissl, OCH solutions at different molecular weights (MW; 2, 5 and 10 kDa) or concentrations (0.3, 0.7 and 1.0 g L-1) were sprayed for four times during the fruit growing season. Results showed that disease incidence and lesion area in the jujube fruit inoculated with M. fructicola and A. alternata were all remarkably reduced by the preharvest OCR sprays, regardless of MWs or concentrations. OCH sprays also significantly (P < 0.05) reduced postharvest natural decay, delayed skin color changing and firmness decline in the jujubes during the storage at 0 degrees C and 80-90% relative humidity. Biochemical evaluations revealed that activities of the main defense-related enzymes, including peroxidase and beta-1,3-glucanase, were significantly enhanced (P < 0.05) in the jujube fruit at harvest and during the storage by the OCH spray. The OCH spray increased superoxide dismutase activity but decreased catalase activity, increased ascorbate peroxidase activity and glutathione content in the fruit. These results suggested that OCH might trigger several defense responses in the jujube fruit against pathogenic infection. Preharvest OCH foliar spray could be a viable alternative to conventional control of postharvest diseases and improvement of storage quality of horticultural products. (C) 2012 Elsevier B.V. All rights reserved.