Microbial secondary metabolite induction of abnormal appressoria formation mediates control of rice blast disease caused by Magnaporthe oryzae

摘要

Okinawa, the only subtropical area in Japan with numerous island ecosystems, is expected to have diverse microbial resources. Recently, we reported the construction of a culture filtrate library with microbes originally isolated from soils in Okinawa, including the Yaeyama Archipelago, and validated its phylogenetic diversity. In the present study, we investigated the inhibitory effect of the cell extract (CE) from microbial isolate 3-45 against Magnaporthe oryzae in rice (Oryza sativa). Abnormal appressorium formation by M. oryzae was induced in the presence of the CE from isolate 3-45. Additionally, melanization of appressoria was inhibited in the presence of CE from isolate 3-45. Sequence analysis of the 16S rDNA region of isolate 3-45 indicated that it shared similarities with Streptomyces erythrochromogenes. When rice leaves were inoculated with M. oryzae in the presence of CE from isolate 3-45, blast lesion formation was inhibited compared to leaves treated with M. oryzae in the absence of CE from isolate 3-45. In addition, M. oryzae infective activity was significantly inhibited in rice leaf sheaths treated with CE from isolate 3-45. Furthermore, abnormal appressorium formation was observed in the presence of heat-treated CE from isolate 3-45. These results suggest that CE from isolate 3-45 can protect rice from blast disease caused by M. oryzae. Further studies are required to identify the active compounds present in 3-45-CE and to clarify its mechanism of inhibition in full detail. The present study on isolate 3-45 might contribute to the development of a new fungicide for controlling rice blast disease caused by M. oryzae.