A potential of Simplicillium subtropicum for biological control against Asian soybean rust
Takuma Nada1* and Izumi Okane2
1Degree Program in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 Japan
2Institute of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
Asian soybean rust (ASR) caused by Phakopsora pachyrhizi (Pucciniales) is a serious disease of Fabaceous plants. In previous studies, several fungal agents against ASR have been reported in the Cordycipitaceae. Some of them are mycoparasitic to rust fungi. Among them, Simplicillium lanosoniveum is known as a mycoparasite against urediniospores of P. pachyrhizi. Other Simplicillium spp. are also expected to possess ability to parasitize P. pachyrhizi or to control ASR by other biological effects. In this study, we aimed to screen Simplicillium isolates that suppress ASR by selectively and effectively collecting mycoparasitic and/or uredinium associating Simplicillium. We inoculated urediniospore suspension of P. pachyrhizi to trifoliates of soybean plants. Detached leaves cut from the trifoliates were cultivated in a square-shaped plastic petri dish at 23 ℃. After 3 weeks cultivation, we found Simplicillium-like colonies, thrips, and mites on uredinia of P. pachyrhizi formed on detached leaves. We isolated those arthropods and hyphae of the fungal colonies, and inoculated them on a LCA plate with chloramphenicol added. As a result, we succeeded to collect several candidates and identified five species and six strains of Simplicillium based on DNA sequences of the ITS/D1D2 region. We co-inoculated the urediniospore suspension of P. pachyrhizi and the conidial suspension of each Simplicillium isolate to soybean plants. As a result, the leaves inoculated with Simplicillium subtropicum strain Th5 significantly decreased the number of uredinia compared to the control. This study indicates the S. subtropicum isolate to be a potential biological control agent against ASR.