Study On The Production And Formulation Of Conidia Of Helminthosporium Gramineum Rabenh F. Sp. Echinochloae

Helminthosporium gramineum Rabenh. f. sp. echinochloae (HGE), is a pathogenic fungus strain isolated from the naturally infected barnyardgrass plant. HGE was found to be safe for agronomically important crops such as rice (Oryza sativa L.), wheat (Triticum aestivum L.), maize (Zea mays L.), cotton (Gossypium spp.), and oilseed rape (Brassica napus L.). Field experiments showed that the conidia of HGE displayed excellent pathogenicity on barnyardgrass and other weed species, and increased the rice yield without negative impacting the rice. These primary studies showed that HGE was a potential mycoherbicide for the control of barnyardgrass in agricultural cropping systems. Currently, a significant constraint to the commercialization of HGE as a bioherbicide is the difficulty in mass production of the conidia and formulation. In this paper, the objective is to achieve conidia production above 10⁷ conidia/g dry material by optimizing the medium and culture conditions in a solid-state fermentation system. Meanwhile, in the process of mass production of conidia, the conidia yield and conidial quality should maintain a high level, which lay a solid foundation for the industrial production. Then four adjuvants that have no effect on conidial germination and mycelial growth are screened by biocompatibility. The formulation of bioherbicide could reduce the reliance on extended periods of moisture, stimulate the conidial germination, enhance toxicity of conidia, increase the ability of diffuse and adhesion, protect pathogen propagules from UV radiation. Many believe that improvement in formulation of biohebicides may provide the key elements to increasing success of the agents in the field and as the formulation may have a great effect on the shelf life of production, it will also affect the development, registration and commercialization. The main contents of this dissertation are as follows:Solid-state fermentation for production of the conidia of HGE. High conidia yield was obtained when the medium consisted of 4g rice flour, 1g soybean meal, 0.2g Na₃PO₄·12H₂O, 0.1 g MgSO4·7H2O and 100mL perlite. Production of HGE conidia was optimized at 76.5% medium moisture, 8% inoculum concentration, 28℃, and 14d incubation. With these optimum medium and culture conditions, the maximum conidia yield was 1.2×10⁷ conidia/g dry material.Solid-state fermentation for mass production of the conidia of HGE. The mass production of conidia of HGE was cultured in trays with the optimum medium and cultivation conditions. The results showed that the maximum conidia yield was up to 1.45×10⁷ conidia/g dry material by tray cultivation, the moisture of conidia powder was 7%⁸%, the conidia number of conidia powder was 3.02×10⁷ conidia/g and the germination rate was above 99%. The conidia yield and quality could come up to the standard by mass production and be as the raw material in the formulation.Study on the formulation of HGE. It was studied that perlite had no effect on conidial germination and mycelial, and when conidium(mg):perlite(mg) was 3:1, perlite stimulated germination without detrimental effects on mycelial growth. Soybean oil had no effect on mycelial growth and stimulated germination as conidium(g): oil(mL) was 2:1. The responses of HGE were highly variable to different surfacetants and stabilizing agents. By detecting their decentralization capacity, suspended rate, stability and biocompatibility, SP-20 as surfacant and CMC as stabilizing agent were determined. The formulation optimizing by quadratic general spinning design was that 33g perlite, 25mL bean oil, 49g CMC and 10g SP-20, synergist A 0.66g synergist B 2.6mL were added into 100g conidia powder,...