Cell-wall Degrading Enzymes Produced By Rhizoctonia Solani And Their Pathogenicity To Rice Plants

The crude cell-wall degrading enzymes(CWDEs) produced by Rhizoctonia solani Kuhn in improved Marcus's medium were extracted when the cultured filtrate was centrifugalled and then the supernatant was reserved. Polygalacturonase (PG), cellulase (Cx), pectin methylgalacturonase (PMG), polygalacturonic acid trans-eliminase (PGTE) and pectin methyl trans-eliminase (PMTE) were determined in the crude enzymes. Among the CWDEs, the activities of PG, Cx and PMG were significantly higher than the others'.The culture condition for the production of Rhizoctonia solani CWDEs was studied. It was appropriate for the CWDEs production as follows: The strains was cultured for 6 days at 28 C in the improved Marcus's medium, in which pH value was 5, without shaking.Rice plants were inoculated by placing a block of the mycelia on the sheath. The activities of CWDEs were determined respectively in three parts of lesion, such as the withered, the brown and the fading. There were five CWDEs mentioned above in three parts of lesion. Among the CWDEs, PG's activity was the highest with 21.123U/mg; the next was PMG; the activities of PGTE and PMTE were lower with about 0.1U/mg. Among the different parts of lesion, the activities of CWDEs in the fading part were the highest with 13.417U/mg; the next was the brown with 11.765U/mg; the lowest was the withered. It suggested that pathogen's CWDEs played an important role in the spot forming and expanding.The CWDEs of Rhizoctonia solani have prominent damage effect on the cells and tissue of rice. Treated by the crude enzymes, the sheath of rice seedling was yellowing and presented watery lesions. The microscope abservation showed that the crude enzymes could destroy the callus cells of rice. Treated by the crude enzymes 24 hours, a part of cell wall was distorted, cleared up or appeared microfibrillate; treated by theenzymes 48 hours, cell wall was cracked and cytoplasm was vastly discharged. Under TEM the crude enzymes could also destroy the sheath cell of rice seedling. Treated by enzymes 36 hours, cell appeared plasmolysis, with cell wall broken fractionally, organelle distinguished unclearly, chloroplast and mitochondria damaged.The CWDEs of Rhizoctonia solani have obvious damage to the cell membrane of rice sheath. Treated by enzymes, the osmosis of cell was changed. In general, the activity of mixed enzymes was higher than that of single enzyme and activity of pectinase was higher than that of cellulase.The production ability of CWDEs was definitely different among the isolates. It was found that there was a significantly positive correlation between the production ability of CWDEs and the pathogenicity of the isolates. It indicated that the CWDEs of R. solani played an important role in the infection and were primary pathogenic factors.