Mutagensis And Molecular Identification Of Helminthosporium Gramineum For Weed Biological Control

Weeds interference is a serious constraint in agricultural production. Presently, the use of chemical herbicides was an important measure to save the cost and improve the efficiency of the agriculture. But the concern is now being expressed throughout the world about the environmental impact, and effects of the widespread use of chemical herbicides. This has fuelled the current upsurge of interest in biological control of weeds using pathogens. It is increasingly being considered as an alternative to chemical control strategies. This is especially true for sustainable agriculture, where adverse effects of agrochemicals on the environment must be minimized or avoided.The plant pathogenic fungus Helminthosporium gramineum Rabenh f.sp.echinochloae, abbreviated as HGE, had been isolated from diseased barnyardgrass (Echinochloa crus-galli (L.) Beauv.) plants. The isolate showed high pathogenicity and specificity towards barnyardgrass. The rice tested was not susceptible to the fugus. Thus HGE is well suited to be developed as a mycoherbicide for barnyardgrass control. In this project, the conidia of HGE were treated by ultraviolet radiation to improve the yield of conidia and metabolized products.From the mutants, we selected mutant Ml and mutant M3 for which may be utilized in the fermentation.The colonies of Ml are white, loose and with more mycelia, which was obviously different from HGE. The M1 grew faster with a higher mycelia and toxin yields. The dry-weight of mycelia was 7.0g/L and the toxin yield was 15.98 mg/L. The colonies of M3 are black, compact and with few mycelia. which was similar to HGE. The mutant M3 produced 1.21 × 10~7 conidia on a fresh potato dextrose agar plate after culturing for two weeks at 28℃ in dark. The conidia yield was 21 percent higher than that of HGE. They both have better pathogenicity and genetic stablitity, and were safe to crop plants such as rice and maize.The change of hereditary material between M1,M3 and HGE can be proved by RAPD-PCR. The solid substrates that use barnyardgrass plants and rice as primary ingredient for mass conidia production were studied respectively. For mass conidia production, it was better to use barnyardgrass plants as primary ingredient. The substrate were inoculated with mycelial plug and incubated for 10 days at 27℃ in dark. Submerged culture experiments were conducted to determine the optimal medium for rapid producing mycelia and metabolized products of the mycoherbicide. The highest mycelial yield of Ml occurred in No. 3 medium, of which the pH was adjusted to 7. The cultures were grown on a shaker adjusted to 150 rpm at 24℃ for 6 days. The No. 4 medium is good for producing toxin. The pH was adjusted to 7 and the cultures wre incubated at 26℃ for 2 weeks.