Cell Wall Degrading Enzymes Produced By Lasiodiplodia Theobromae (Pat.) Griff.&Maubl And Its Pathogenicity For Longan Fruit

Lasiodiplodia theobromae (Pat.) Griff.&Maubl is one of the main pathogen of latent infection to cause postharvest longan diseases. During the process of pathogenicity, it can produce cell wall degrading enzymes (CWDEs). CWDE is an important pathogen factor in causing plant diseases. The material of this experiment named Lasiodiplodia theobromae (Pat.) Griff.&Maubl was isolated from longan pulp. In this paper, the fermentation condition, pathogenicity and the effects of phenolics for Lasiodiplodia theobromae (Pat.) Griff.&Maubl CWDEs were all studied. The results were summarized as follows:1. The CWDEs such as exo-1,4-β-D-glucanase (Cx), β-glucosidase, polygalacturonase (PG) and pectin methylgalacturonase(PMG) were produced in improved Czaper medium by Lasiodiplodia theobromae (Pat.) Griff.&Maubl. The factors including the cultural time, the cultural temperature, the original pH value, the carbon source and the nitrogen source were studied for producing cellulase and pectinase by Lasiodiplodia theobromae (Pat.) Griff.&Maubl. The results showed that the optimum cultural time was6d, the optimum cultural temperature was28℃, the optimum original pH was7.0, the optimum carbon source and nitrogen source was2%powder of longan pericarp and0.2%NH4H2PO4. Using the culture time, the original pH, the carbon source and the nitrogen source to design L16(45) orthogonal experiment and found the optimal fermentation condition of Lasiodiplodia theobromae (Pat.) Griff.&Maubl. The results showed that the optimum cultural condition for Cx were:the culture time was6d, the original pH was6.5, the carbon source was1.5%, and the nitrogen source was0.2%. The optimum cultural condition for PG were:the culture time was7d, the original pH was7.0, the carbon source was1.5%, and the nitrogen source was1.0%.2. The CWDE of Lasiodiplodia theobromae (Pat.) Griff.&Maubl have obvious damage to the cell membrane of longan pericarp. Afrer treated by cellulase, pectinase and mixed enzymes, the osmosis of cytomembrane of longan pericarp increased. The mixed enzymes’lesion rate was48.11%, its damage was the most prominent. The leion rate of cellulase and pectinase were36.68%and36.16%. The CWDE of Lasiodiplodia theobromae (Pat.) Griff.&Maubl have obvious damage to the pericarp tissue of longan fruit. Treated by the enzymes of pectinase, cellulase and mixed enzymes, the longan pericarp tissue were brown and presented macerated? The symptoms of leaves treated with mixed enzymes were more serious than that of longan trested by pectinase and cellulase.After Lasiodiplodia theobromae (Pat.) Griff.&Maubl infected longan fruit, four kinds of CWDEs (Cx,(3-glucosidase, PG, PMG) could be examined, and the activity of PG was the highest. However, among different part of diseased longan pericarp the activity of CWDE’s activity was also different. It was found that the CWDE’s activity was the highest around the boundary between diseased and healthy areas. And the next was diseased areas, the last was healthy areas.3. The results of the research showed that lower concentration of pyrocatechol (0.2mg/L-0.5mg/L), phloroglucinol (0.2mg/L-2.0mg/L) and anillin (0.2mg/L-2.0mg/L) were all capable to induce Lasiodiplodia theobromae (Pat.) Griff.&Maubl to produce CWDE. And along with the phenolics’ concentration increased, CWDE’s production decreased. Pyrocatechol, phloroglucinol and vanillin were all capable to inhibit the producion of CWDE. Their inhibiting concentrations were5.0mg/L,10.0mg/L and10.0mg/L. Pyrocatechol, phloroglucinol and vanillin were all capable to inhibit the activity of Lasiodiplodia theobromae (Pat.) Griff.&Maubl CWDE. Vanillin showed the strongest inhibiting ability, when its concentration was10mM, the four kinds of enzymes (Cx, β-glucosidase, PG, PMG) were all inhibited. Pyrocatechol and phloroglucinol were the next, inhibiting concentrations were200mM and1000mM.