Antifungal Activities and Stability of Metabolites from Streptomyces rochei YL-2 Against Pyricularia oryzae

A strain of endophytic actinomycete(YL-2) was isolated from the leaf of Azadirachta indica A. Juss and was identified as Streptomyces rochei. It exhibited antagonistic activities against Pyricularia oryzae. Different solvents were used to obtain the crude extract, and ethyl acetate was shown to produce active substance with strongest inhibitory effect against Pyricularia oryzae showing an inhibitory diameter of 24.2mm. The methods of suspending and mycelium growth rate were adopted to study the effect of concentration of crude extract on Pyricularia oryzae. Results indicated that the inhibitory effect of the crude extract on spore germination of Pyricularia oryzae increased as concentration of crude extract increased. The max spore germination inhibition rate in 0.8g·L-1was 97%, and the mycelium growth inhibition rate in 1.6g·L-1was 92.2%. The stability of the crude extract was tested against heat, acid, alkali and sunlight. The inhibition effect decreased significantly as the temperature increased. The maximum inhibitory diameter was 27.5mm at room temperature. The crude extract had higher stability in weak acidic environment showing highest stability at pH of 4.0. The crude extract also had a low stability when exposed to sun light. It was highly sensitive to light and gradually lose its activity when exposed to light.