| At present in China, reports of mycoherbicide research mainly focus on the isolation and screening of the potential pathogens, or focus on some characteristics evaluation for weed biocontrol. In this project, we integrated evaluate the potential biological control fungus Helminthosporium gramineum Rabenh f. sp. echinochloae (HGE) of baryarndgrass {Echinochloa spp.) from follow aspects: the fungus' morphology, biological characteristic, epidemiology, host range, mycotoxin, pathogenicity mechanism, technology and method for mass conidia production and substrates screening. Preliminary improvement of HGE fungus is conducted by using the technology of physical (including ultraviolet and nucleus) radiation, chemical induction combine with biotechnology of protoplast fusion. A good foundation is laid of using HGE fungus to develop bioherbicide through the above researches. The main results are as follows:1. Four pathogens with characteristic are selected from more than ninety baryarndgrass fungi. They are Alternaria alternata (in breviation AA, the followings are as the same)/ Curvularia lunata (CL) , Exserohilum monoceras (EM) and Helminthosporium gramineum Rabenh f. sp. echinochloae (HGE). After comparison study on morphology, biological characteristic and host range testing, the HGE fungs is chosen as potential biocontrol pathogen of baryarndgrass. The HGE fungs belongs to the Drechslera Ito (Bipolaris Shoemaker), Dematiaceae, Hyphomycetales.2. The colonies of HGE fungs are dark or dark to brown, compactness and with few hypha. The conidia's colour is yellow brown to brown, cylinder to spindle shaped, the cell of both sides of the conidium is obtuse round. The size of conidium is 17.0-21.3 um width and 62.5-102.5 urn length with 2-6 septa. The sporulation ability of HGE fungs is higher than that of EM but lower than CL fungus. Abundance mycelia can beproduced in fermentation culture in both barnyardgrass decoction dextrose liquid (BDDL) and modified Fries liquid (MFL).3. Temperature, illumination, pH valuve and aeration (means with enough oxygen) are provided with significant affect on HGE fungs' growth and sporulation. The optimal conditions for growing and sporulation of HGE fungus are 28C, in dark, slight acidity (pH 6.0-6.5) and with aeration. The HGE fungus is sensitivity to high temperature. Growing and sporulation of HGE are significantly restrained as the temperature is higher than 30C. The Echinochloa species of beardless barnyardgrass [Echinochloa crusgalli (L.) Beauv. Var. mitis (Pursh) Peterm], junglerice [E. colonum (L.) Link] and Taiwan barnyardgrass (E. glabrescens Munro ex Hook. F.) are highly sensitivity to HGE fungs, while barnyardgrass (E. crusgalli (L.) Beauv) is middle sensitivity. Except slightly infected sorghum and barley seedlings, for more than ten tested crops, including the grass, legume and cruciferae family, can not be infected by HGE fungs (that means HGE fungs is safty to these crops).4. HGE fungus shows higher pathogenicity to baryarndgrass while good conditions are required for its epidemiology. Spraying with HGE spores concentration of 2.5x107/M2, keeping the tested seedlings in 25-28C, over 95% of relative humidity (RH), 12-18 hours dark conditions after inoculation, infected plants and plant mortality rate is over 85%, and over 75% dry weight control efficacy can be reached to 1.5-2.0 leaf stage baryarndgrass. Infected plant rate of HGE fungus to 1.0-5.0, plant mortality to 1.0-3.0 leaf stage of baryarndgrass are over 80% and 85%, respectively. The highest dry way control efficacy of HGE fungus to baryarndgrass is over 83% at 3.0 leaf stage.5. HGE fungus can produce black toxins on PDA media. It also can produce host specific toxins in both modified Fries liquid (MFL) and Barnyardgrass decoction dextrose liquid (BDDL) for fermentation on a shaker. The pathogenicity to baryarndgrass is stronger of spraying toxins mixture with conidia suspension, or succesively spraying toxins and conidia suspension than their application respectively. Part... |
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