Study On Biological Evaluation And Utilization Of Pathogenic Fungi In Echinochloa Species

Four species of pathogenic fungi were isolated from naturally infected Echinochloa species, and evaluated as biological control agents of Echinochloa species in rice. Curvularia lunata could produce a great number of conidia but was pathogenic to both rice(Oryza sativa L.) and barnyard grass(Echinochloa crus-galli (L.) Beauv. Var. mitis (Pursh) Peterm.). Alternaria alternata could also produce a large number of conidia but was low pathogenicity to barnyard grass. Exserohilum monoceras and Drechslera monoceras were both high pathogenicity to barnyard grass and safe to rice. D. monoceras could produce more conidia than E. monoceras did. Thus D.monoceras was selected as a potential bioherbicide for biological Echinochloa species control.Conidia of D.monoceras germinated rapidly when inoculated on PDA media and started to produce new conidia at 66h after inoculated at 28"Co The optimal temperature and pH value for radical mycelia growth and conidia production of D. monoceras on PDA were 28 and pH6~7, respectively. Light inhibited conidia production of D. monoceras. The best sporulation occurred under continuous dark conditions. Ample supplies of air greatly increased radical mycelia growth and conidia production of D. monoceras. High-yielding conidia strain 1262 and auxotrophic strain 1004 were screened by treated initial strain of D. monoceras with 0.2mg/ml NTG for 20min. D.monoceras FII 116 FII 121 and FII 140 which can produce more conidia than strain 1262 does, were isolated after treated 1262 with r-ray. None of fusion products from protoplast fusion between inactivated protoplasts of C. lunata and protoplasts of auxotrophic strain 1004 was obtained. The effects of factors, such as culture age, lytic enzyme concentration, osmotic stabilizer, pH value of buffer solution and digesting temperature, on the formation of protoplast of D. monoceras 1004 and C. lunata were studied. Maximum yield of protoplast of strain 1004 could be obtained with mycelia cultured for 42h by using 2% Lywallzyme and 2%Cellulase (pH4.4~5.8) containing O.Tmol-L"1 KC1 as osmotic stabilizer and digesting for 4h at 30.While the maximum yield of protoplast of strain C.lunata could be obtained with mycelia cultured for 18h by using 2% Lywallzyme and 4% Cellulase (pH5.8) containing O.Tmol-L"1 KC1 as osmotic stabilizer and digesting for 4h at 30癈. The regeneration of the protoplast of D. monoceras and C. lunata was tested on the solid media containing osmotic stabilizer and regeneration rate was 0.15% and 0.76% respectively.Of 7 agricultural-based products evaluated as solid substrates, the most abundant sporulation of D. monoceras (4.17*106 conidia/g of dry weight) occurred on barnyard grass substrates. The conidia production of D.monoceras was affected by inoculation method and moisture content.