Research On The Screening And Antagonistic Mechanism Of The High Effective Biocontrol Trichoderma Against Phytophthora Parasitica Var. Nicotianae

Twenty strains of Phytophthora parasitica varnicotianae are collected and isolated in the fields infected with Phytophthora parasitica varnicotianae from Ningxiang, Yongzhou,Chenzhou and Xiangxi(West Hunan) in Hunan Province, on which virulence determination is conducted. Among them,12 strains of stronger pathogenicity are screened, followed by DNA extraction and cloning and sequencing, so as to create the final phylogenetic tree. The results show that the differences between the 12 species are extremely low, with close genetic distance (far less than 0.05) and basically no variation between individuals.Sixteen species of Trichoderma were isolated from different soil types collected from different parts of Hunan Province, and a preliminary identification is conducted on them. Through confronted cultivation with tested pathogens, and judging by their growth rate, the rescreened T2-16 tested has stronger competition and parasitism, characterized by fast growth, more sporulation and broad antibacterial spectrum.Researches on the antagonistic mechanisms of T2-16 Trichoderma strains show that the T2-16 has a stronger nutrition competition and space competitiveness. Through the plate cultivation of T2-16, it is determined that antibiotic andβ-1,3 dextran sugars and cellulase enzymes are created out of them, which inhibit the growth of Phytophthora parasitica varnicotianae.All the selected Trichoderma strains are screened on the good fermentation conditions, the results of which show that the optimum temperature for Trichoderma cultivation is 25-28℃and light has no effect on mycelial growth of Trichoderma but a significant effect on spore germination, and when pH value is at 5-6, it features fastest growth and highest spore germination rate. Lactose is also identified as the best carbon source while asparagine the best nitrogen source.A dynamic study on the antagonistic Trichoderma in the soil, leaf and root shows that Trichoderma is strongly inhibited on the surface of the unsterilized soil, but the inhibitory effect is very low in unsterilized soil. T1-16 in the tobacco leaf surface is most commonly colonized in the pores, recessed areas on leaves. When the water content reaches 3%, T1-16 colonization peaks and acidic environment is conducive to the growth of T1-16 and colonization.