Induced defense responses against Rhizoctonia solani in rice seedling by a novel antifungalmycin N2 from Streptomyces sp. N2

Abstract

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N), was a novel and broad-spectrum antifungal metabolite produced by Streptomyces sp. N2. In the present work, antifungalmycin N2 was evaluated its induction of resistance against Rhizoctonia solani in rice seedling by measuring the defense-related physiological and biochemical parameters, such as the production of reactive oxygen species (ROS), the enzymatic activities involved in antioxidant systems (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD), phenolics metabolism (phenylalanine ammonia-lyase, PAL; polyphenol oxidase, PPO), and pathogenesis-related proteins (β-1,3-glucanase and chitinase). It was found that the percentage disease index (PDI) of the R. solani-inoculated rice reduced from 65.21% to 26.02% when treated with 5.77 μg/ml antifungalmycin N2. Further results showed that the rice seedling could trigger its defense responses to R. solani infection by sharply accelerating the accumulation of ROS such as ·O2¬ and H2O2. But when the R. solani-inoculated rice was treated with antifungalmycin N2, the antioxidant SOD, CAT, and POD were significantly induced during the whole period of post inoculation (24–96 h), and consequently resulted in a sharp decline of ·O2¬ and H2O2 in rice seedlings. Compared with the R. solani-inoculated rice, the enzymatic activities of PPO, PAL, β-1,3-glucanase, and chitinase were significantly enhanced in the rice treated with antifungalmycin N2 plus R. solani. In conclusion, the above results suggested that antifungalmycin N2 could induce the resistance against R. solani in rice seedling by stimulating a series of defense responses, which would provide a comprehensive insight into the biocontrol function beyond its direct antagonistic activity against plant fungal pathogens.