| The potato late blight, caused by Phytophthora infestans (Mont.) de Bary, is one of destructive diseases in agricultural production which resulted in economic loss as 6.5-13 billion Chinese currencies for each year. So characterization and identification of specific antagonistic fungi against Phytophthora infestans is a potential controlling stragetey.The Fungi Geomyces sp.WZJ was occasionally found to inhibit the growth of P. infestans in our laboratory when we cultured P. infestans. It was isolated to further study. By using dual culture agar plate assays, the strain showed the similar inhibitory efficiency ranged from 64.4% to 78.5% with 13 strains of P.infestans. Meanwhile, we tested the antifungal spectrum of Geomyces sp.WZJ too, the results showed that it had a good antagonistic effect on P. capsici, P. sojae and P. nicotianae as well as to P.infestans. But it showed poor inhibitory effect for other test fungal pathogens causing the different plant diseases. This was suggested that the strain had specific antagonism of Phytophthora species.Based on morphological and molecular biology methods, the strain was identified as Geomyces sp. and named as Geomyces sp.WZJ. Biological characteristics studies showed that the strain could grow normally in PDA, PSA and RA medium, but not in Czapek medium, which show the smallest diameter of mycelium. It was identified to grow best on PSA with the biggest diameter of mycelium and more number of spores genereated. It could grow ranged from 4 to 25℃, and the optimum temperature is 18℃ which suggested for low temperature growth. Also, it was not strictly required for the pH value, and the optimum pH value for its growth is about 6.In order to character the antimicrobial metabolism substances for Geomyces sp.WZJ, the inhibition effect against P. infestans has been investigated in this study. After cultrured with potato sucrose broth, the water extracts of supernatant had strong antagonistic effect against P. infestans, while the extraction from dry mycelia had no antimicrobial effect, indicating that the inhibitory substances were secreted into the extracellular.The inhibitory efficiency of sterile fermentation supernatant was then detected by the growth rate method. The results showed that the inhibitory efficiency is 35.6% when mixed the volume of 5 days sterile fermentation supernatant of fermentation with rye medium at ratio of 1:25. And the inhibitory efficiency is increased to 93.6% for 10 days sterile fermentation supernatant of fermentation. This is indicated that within a certain time frame, the antimicrobial substances gradually produced with the increased of the number of days of fermentation, The "IC50"of 16 days sterile fermentation supernatant was measured as 176-fold dilution.The general characteristics of the antimicrobial substances have been prelimitary studied. It is soluble in water and tolerance to high temperature. There has no antimicrobial activity detected for the components of fatty substances and polysaccharide, indicating that the bioactivity substances do not belong to fatty or polysaccharides.We tested the protection ability of the sterile fermentation supernatant against potato late blight in vitro by using detached leaves assay. Compared with the mock prespraying with cultrural medium only, the biomass of P. infestans quantified by quantitative real-time PCR suggested that it was 122 times less in pre-spraying sterile fermentation supernatant leaves than in the mock treated leaves. |
PDF Full Text Request