| Potato late blight caused by Phytophthora infestans (Mont.) de Bary is one of the most serious diseases in potato production in all over the world. It is well known as the first crop disease since the damages and losses of this disease are much heavier than that of rice blast and wheat rust diseases, as well as difficult to control. Previous experiments conducted in our laboratory showed that both fermentations of Alternaria kikuchiana and Alternaria brassicae had significant suppressions on growth of P. infestans. And the inhibition rate of mixed fermentation together as 1:1 ratio from single fermentation of A. kikuchiana and A. brassicae was higher that of single fermentation. In order to make it clear that control of this disease by active substances from above mentioned antagonistic fungi, the feasibility and conditions in compound fermentation of two species of fungi and stability of antagonistic substance in compound fermentation filter were investigated based on former experiment results, and the main results were as follows.(1) It was definite that there was no antagonistic or depression between two fungi by dual culture method, and they could grow together completely on PDA medium. Therefore, compound fermentation of two fungi could be conducted.(2) The conditions of compound fermentation of two fungi were tested and optimized. The best compound fermentation conditions against P. infestans was as follows:the fungi were cultured at 25℃in dark and standing status on PDA medium with primary pH value of 6.29 (natural pH value) for 4 d.(3) To have made it clear that repression effect of different compound fermentation concentrations on P. infestans. The inhibition rate of compound fermentation was 92.15% as concentration 7 mg/mL at optimized conditions, which was much better than that (89.8%) of mixed fermentation together as 1:1 ratio (concentration of 10 mg/mL) from single fermentation of two fungi. It indicated that compound fermentation of two fungi might produce some cooperation or synergism, which resulted in more effective inhibition to P. infestans. (4)The effects of temperatures and pH values on inhibirory effect of active substances in compound fermentation were measured based on filter paper method. To compare with control, the inhibition effect of all compound fermentations after treatment with high temperature decreased in some degree, but the inhibition rate with treatment of 121℃still could reach 66.78%, which suggestted that it could still remain inhibition activity of 73%. The inhibition effect of compound fermentation treatmented with different pH values also displayed descending phenomena, however, the inhibition rate with treatment of pH2 still was 68.67%, that indicated activity of 75.5% still conserved. These results showed that antagonistic substances in compound fermentation liquor had strong thermostability and well resistance to superacid and strong alkali.(5)The possible antagonistic mechanisms for compound fermrntation against P. infestans were investigated by morphological observation of mycelial and protein content measurement. The phenomena of protoplast aggregation or gathering together, mycelial thickening or thining, were only found in mycelial treated with compound fermentation. And soluble protein content in mycelial treated was lower than that of untreated mycelial. It manifested that the some substances in compound fermentation liquor possiblly could supress the protein biosynthesis in treated mycelial. |
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