Period And Mechanism Of Latent Infection Of Postharvest Alternaria Rot (Alternaria Alternata) Of Apricot Fruit (cv.LanZhou Dajiexing) And Its Control

Alternaria rot of apricot cv. Lanzhou Dajiexing (Armeniara vulgaris Lam.) caused by Alternaria alternata (Fr.)Keissl. occurred as the main disease which was up to 93.2% of the total decay during storage. Isolation of latent fungi from buds, floral parts and fruit of apricot during growth showed that A.alternata initially infected styles and settled in ovary and keeped quiescnt during flowering. A.alternata infected young fruit through the epiderm but was limited in the subepidermal layer, and levels of infection by A.alternata varied with zones of the peel from stilar end to the stem end of the fruit during enlargement. At harvest the stilar end of the peel was infected higher than other zones. The isolated A.alternata from the peel of the young and healthy fruit only caused the ripe fruit to dacay but not the unripe. This result indicated that preformed antifungal compounds presented hi the unripe fruit peel. TLC- A.alternata bioassay of the methol-dichloromethane crude extract taken from unripe fruit peel demonstrated two inhibition spots. Compounds from the spots was analysed with gas chromatography and mass spectroscopy (GC-MS) and 7 compounds was identified as dodecyl acrylate, hexadecanoic acid, diisooctyl adipate, 2,6,-bis (1,1-dimethylethyl) -4-(methoxymethyl) - phenol, di-n-octyl phthalate, squalene (or farnesol), bis (2-ethylhexyl) phthalate. Among them the squalene and diisooctyl adipates was proved A.alternata inhibition in vitro. The preformed antifungal compounds declined gradually with the fruit development, and little compounds were detected till harvest. Lipoxygenase (LOX) was involved in the progress of maturation of the fruit. LOX activity increased with the fruit developed from unripe to ripe. Measuring LOX activity of the fruit wounded- inoculated with A.alternata showed LOX activity was related with the spreading of lesions. The activity increased and maintained at a higher level during infection. From 2 weeks after flowering, Imazalil and Maneb was sprayed periodically to the fruit teers. The treatments obviously decreased the rate of latent infection of A.alternata to the fruit during growth. At the time, the treatments decreased decay of the fruit stored at low temperature, and 0.1% Imazalil was found to be more effective to inhibit the infection and decay. Moreover, postharvest Imazalil treatments also decreased decay of stored fruit and at 250ppm the result was better. However, SOOppm Imazalil injured the fruit. Postharvest non-fungicide treatments with 2.0%CaCl2,0.3g/L Salicylic acid (SA), 1.0%Chitosan and 45 癈 hot water inhibited lesion spreading of the wounded-inoculated fruit, and decreased LOX activity.