| The chemical weed-control had made large contribution to the development of agriculture.But the environmental pollution, increase of weed type with resistance against herbicide and safety of agricultural products came with the use of the chemical herbicide. Therefore, the new type herbicide had to be developed to reduce the usage of the tradiontal chemical herbicide, which was the trend of agriculture in future. Expending microherbicide, biologically control the weeds would reduce the usage of chemical herbicide, then to realize the sustainable development of the agriculture.Helminthosporium gramineum Rabenh f. sp. echinochloae and Curvularia lunata were isolated by the China National Rice Research Institute, which were fungal pathogens of the barnyargrass from the natural infected weed plants and had potentials to develop into biological agents. HGE strains had high virulent to the barnyardgrass but low spore yield, while the CL strain had high spore yield but low virulent to the weed. The objectives of this study was to combine the advantages of the two strains into new ones by protoplast fusion, which provide higher spore yield and richer toxin, as well as to the favor of industrial production, then to study the procedures to make the microbe emulsion of the crude toxin, and to investigate its efficiency to control weeds in rice fields. The major results of the study showed as follows:1. The optimal condition for protoplasts releasing was decided as that the most effective lytic enzyme mixture for CL was 2% lywallzyme plus 2% snaiiase and that for M1 was 2% cellulase plus 2% snaiiase, that the optimum incubation time was 16 h for CL and 24 h for M1. The protoplasts were regenerated in the liquid regeneration medium and gave a high regeneration frequency, which was 14.70%±1.27% for CL and 11.11%±1.43% for M1.2. The protoplast fusion process gave a high fusion frequency, which was 2.6×10-3 between M1 and CL,2.1×10-4 between M3 and CL. There were four fusant strains that improved toxin production, especially for CM1-037, which gave a 1.34 times ophiobolin A production than its parent strain M1. And there were two fusant strains between M3 and CL, which gave a higher spore yield and improved biologolical control efficiency against barnyardgrass in greenhouse, and its fresh weight control efficiency and dry weight control efficiency of the fusatnt strain CM3-012 and CM3 - 053 were 1.77% and 4.89%, 9.73% and 12.55% respectively higher than their parent strain.3. RAPD analysis on the relationship of fusant strains and the parent strains showed that genetic recombination occurred during protoplast fusion.4. The condition for toxin production was that CM1-037 as strain, potato 200 g/L, glucose 30 g/L, wheat bran 20 g/L, yeast extract 1g/L, KH2PO4 2g/L, MgSO4.7H2O 1g/L as medium, and mycelia 10 ml/L as inoculums.5. The 10% crude toxin microbial emulsion were that 10% crude toxin + 8% solvent 9# + 7% solvent 5#+4.5% emulsifying agent 1# + 10.5% emulsifying agent 9#+ 2% lanrocapran+58% water, which had a high efficiency control weeds such as false loosestrife, indian rotata, Sedge. When combination with the low usage of chemical herbicide ( bensulfuron methyl + quinclorac) , it improved the efficiency against barnyardgrass and Monochoria above 80%, against false pimpernel above 75%.
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