Study of control systems for soil-borne diseases by indigenous microbial diversity

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In controlling plant diseases, utilization of natural and safe microorganisms for biological control system is highly anticipated. However, this disease control system is often claimed for its inconsistent effect. Therefore, we conducted a series of experiments aiming at development of disease control systems pertaining safe and consistent efficacy for soil-borne diseases by utilizing indigenous microbial diversity. Specific results obtained in this research projects are as follows. (1)Analysis of relationships between soil-borne diseases and microbial diversity indigenous to soil : application of wild oats as a green manure, which was effective on controlling Verticillium wilt of tomato in previous pot experiments, was verified under a field condition in monitoring soil microfloral changes with PCR-DGGE, FAME, and CLPP. On the other hand, suppression of Fusarium wilt and Bacterial wilt of tomato by applying wheat-bran with irrigation, i.,e., ‘soil disinfestation with soil reduction me … More thod' was investigated in terms of pathogen densities as well as facultative anaerobic bacteria. The latter was further elucidated with identifying bacteria by cloning the DGGE bands. In addition, organic acids produced during this event were determined with HPLC. (2)Analysis of relationships between soil-borne diseases and symbiotic arbuscular-mycorrhizae (AM) diversity indigenous to soil : AM are known to protect plant from various environmental stresses as well as provision of inorganic nutrients such as phosphorus. Therefore, to elucidate the relationships between AM diversity indigenous to soil and suppression of soil-borne diseases, the AM diversity colonizing plant roots was determined using fatty acid methyl ester(FAME). Specifically, components of FAME originated from AM e.g., 16:1ω5 were compared between healthy and diseased (infected by Verticillium wilt) roots of eggplant. The results indicated that the FAME components of diseased roots substantially differed from those of healthy roots, suggesting that AM fungi indigenous to soil influences on the disease occurrence of Verticillium wilt of eggplant. Less