| Effect of chitosan on Afternaria rot of Pingguoli Pear and its antifungal mechanism were initially investigated. The orthogonal experiment design of four factors and four levels was used to choose the best combination of concentrations, solvents, temperatures and surface active agents. Results showed that: the combination of solvent of 1% acetic acid, surface active agent Tween2O,45 C and the 2% chitosan solution was the best in the orthogonal experiment and that of 1% L-glutamic acid, Tween40, 50C and 2% chitosan was the next. Among the four factors, the inhibiting effect of concentration on the lesion area of Alternaria rot was the most significant, and the higher the concentration, the smaller the lesion area. The effect of solvent was inferior to the concentration, and temperature and surface active agent had little effect. With 1% acetic acid as solvent and Tween2O as surface active agent, the best concentration of chitosan was chosen by dipping the fruits into the chitosan solutions at 45 0C. Results showed that: the lesion area of the fruits treated by chitosan was significantly lower than that of untreated. The difference between chitosan-treatment before inoculation and after was compared. The effect of chitosan-treatment before inoculation on control of Alternaria rot was better than that of after, and the 3% chitosan treatment was the best. Methanol-dichloromethane crude extract from the peel was separated by thin- layer chromatographic(TLC) plates. The isolated preformed antifungal compounds were detected with conidia of Aternaria tenuis Nees and the inhibition zones showed difference between the chito san-treatment and the control. By using gas-chromatography and mass spectroscopy (GC/MS), the compounds in the inhibition zones were separated and identified. Eleven antifungal compounds were induced by chitosan-treatment, including 9- Hexadecenoic acid, methyl ester, Butylated tlydrorytoluene, Octadec-9-enoic acid,Sequalene etc. And fatty acid, methyl ester of different saturation degree was the main composition of the preformed antifungal compounds. The activities of chitinase and P -1,3 -glucanase exacted from intact and cut fruits treated by chitosan of different concentrations were different. The activities of enzymes from intact fruits treated by 2% chitosan were near those of cut fruits treated by 0.75% chitosan, and they were 0.0202 and 0.0203,0.51 and 0.52 respectively. As compared to the control, the activities of chitinase increased by 48.18% and 47.45%, and the activities of P -1,3-glucanase increased by 16.87% and 16.65%, respectively. In vitro, 6.OmgImL chitosan inhibited spore germination of A. tenuis Nees by 79.54%. There was a positive correlation between log percentage of inhibition of spore germination and log chitosan concentration (R2=0.9465). And 6.Omg/mL chitosan inhibited the radial growth by 85.89%, and there was also a positive correlation between log inhibition of radial growth and log chitosan concentration (R2=0.9028). Chitosan of different concentrations induced morphological changes of the hyphae, and when the concentration reached to 3.OmgImL, the hyphal morphology began to change. And the hyphae changed from long and thin to bead-like, and also partly swelled. |
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