Study On Mechanism Of Pericarp Breakdown Of Longan Fruit Inoculated With Lasiodiplodia Theobromae (Pat.) Griff.&Maubl.

Longan (Dimocarpus longan Lour.) is a subtropical valuable speciality with high medicinal value and nutritional value in China, mainly growing in Fujian, Guangdong, Guangxi, Taiwan and other places. Sinse longan fruit mature during the hot and humid summer, Postharvest physiological metabolism is strong, easy to brown and rot, lost food value, seriously restricting the storage and the sales of Longan. Breakdown of longan pericarp inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl. is the main disease of postharvest longan fruit in Fujian. Previous studies concluded that the browning and breakdown of longan pericarp is related to latent infection of the pathogen before harvest.In this study, the materials of this experiment are fruits of longan (Dimocarpus longan Lour.cv.Fuyan), which are inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl. and storaged under room temperature. We researched in active oxygen metabolism, phenolic metabolism, pathogenesis-related proteins and cell wall metabolism, to study the metabolism of pericarp breakdown of longan fruit inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl. The results are as follows:1、Effect of active oxygen metabolism of longan pericarp inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl.:Early inoculation (0-2d), reactive-oxygen-scavenging enzymes (SOD, CAT and APX) activities and endogenous antioxidants contents decreased significantly. Productive rate of O2-increased at the same time. Middle storage(2-4d), a large number of active oxygen scavenging enzyme activity was induced during storage to maintain the balance between free radicals. When the rate of active oxygen scavenging capacity is more than its own, the metabolic balance of active oxygen damage. Accumulation of active oxygen ultimately lead to membrane lipid peroxidation which makes the cell injured or even death.2、PPO and POD activities in pericarp of longan inoculated with Lasiodiplodia theobromae Pat. were so more significant increase that the phenolics had a large number of degradation. PAL activity decreased rapidly at the same time. Thus synthesis of lignin is blocked, which decreased the disease resistance and accelerate the breakdown of longan fruit.3、CHI activity of longan pericarp inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl. increased rapidly in0-1day, which control the disease development in some way and slow down the breakdown of pericarp cause by bacteria. CHI and GLU activities were lower level in3-6day, lead to growth of bacteria in pericarp cells and rot of longan pericarp.4、there were singnificant differences between the longan pericarp cell wall components content, cell wall-degrading enzyme activity inoculated with Lasiodiplodia theobromae (Pat.) Griff.&Maubl. and their own controls. During storage period, longan pericarp cell wall substances, hemicellulose and pectin content was significantly smaller than the control, while PG, PE, Cx activity in the cell wall are significantly higher than the control. These results indicate that the inoculation of Lasiodiplodia theobromae (Pat.) Griff.&Maubl. accelerated degradation of cell wall components by increasing cell wall-degrading enzyme activity, result in disintegration of cell wall and structural damage, thus helping the pathogen expand in the cells. Eventually pericarp crack and decay.