Antagonism Of Pythium Oligandrum And Induce Resistance Of Oligandrin To Pathogens

Most Pythium Pringsheim are plant pathogens, but some species of Pythium not only have no pathogenicity to many crops, but also have antagonism and mycoparasitism against more than 20 important plant pathogens, and also induce resistance in plants. In recent years, the oomycete Pythium oligandrum Drechsler has been the subject of several studies dealing with its potential as a biocontrol agent of soilborn deseases affecting numerous crops of economical importance. In this study, three methods of isolating P. oligandrum were compared. The antagonism of P. oligandrum against some pathogens was primary investigated. Oligandin was purified and its polyclone antibody was obtained. Induce resistance of oligandrin to Botrytis cinerea in cucumber plants and its mechanism was studied. Results were summarized as follows:1. P. oligandrum was isolated from 54 samples of soil using three methods (SSDP, baiting with burying slide in soil and baiting with sprinkling soil). The results showed that P. oligandrum can be detected in vegetable soil, coastal sandy soil, lawn soil and paddy soil. But P. oligandrum was detected more by baiting with sprinkling soil than the other two methods. Three host fungi were used to detect P. oligandrum from soil. P. oligandrum was seen mostly on Fusarium culmorum, less oftern on Botrytis cinerea and never on Rhizoctonia solania.2. Antagonism of P. oligandrum against eight plant pathogens and two athlete's foot pathogens (Trichophyton rubrum and T. gypsum) was investigated by dual culture technique.The results showed that all the pathogens were inhibited by P. oligandrum. Scanning electron microscopy (SEM) revealed that intimate contact between mycelium of P. oligandrum and mycelium of F. oxyporum f. sp. cucumerium resulted in a series of disturbances, including aggregation of host cytoplasm, wall deformations, hyphae fracture, coiling, collapse and turgor, but the hyphae of P. oligandrum were in good health. Similar events were observed during the interaction between P. oligandrum and Trichophyton rubrum or T. gypsum.3. Liquid medium of P. oligandrum, which can stimulate oligandin production, was optimized to be: add 1/2 PDB to PO culture medium. P. oligandrum can secrete more oligandrin in this optimized medium. Oligandrin, with a molecular weight 10KDa and isoelectric point 4.5, was purified by ammonium sulfate grade precipitation followed by SDS-PAGE, and identified by PF-2D. Polyclonal antibody of oligandrin was obtained by immunizing rabbits with antigen treated by three methods (coupled with both EDAC and OVA, coupled with EDAC only, grinding gel). Immunity of antiserum coupled with both EDAC and OVA was better than coupled with EDAC only.4. Potential of oligandrin to induce resistance in cucumber infected by B. cinerea was primary studied. The results demonstrated that the disease index of oligandrin-treated plants decreased significantly. Also, the activities of peroxidase (POD) and polyphenol oxidase (PPO) in oligandrin-treated plants were significantly higher than those in control plants on the sixth day after inoculation.