Biological Control of Brown Stem Rot of Adzuki Bean by Cleaning Crops

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The purpose of this study is to find the effective crops in reducing the Brown Stem Rot (BSR) disease of adzuki bean by the cleaning crops. In 1998 and 1999, 4 green manure crops (vetch, italian ryegrass, wild oats and sorghum) were planted in different fields infested with the pathogens and in the next year, adzuki bean planted in all fields. The disease decreased remarkably in the fields planted with wild oat compared with other crops. However, no relation was found between the pathogen population and the crops. The yields of wild oat planted plots was higher than that of any other crops among green manure crops tested. These results showed the wild oat was the most suitable for cleaning crops to BSR of adzuki beans. To find out the mechanism of the disease suppression by wild oat, the soil microflora in the wild oat planted soils weas cheked. The population of antagonistic actinomycetes to the pathogen was about 13 times higher than the adzuki bean replanting plot soils. The germination of the pathogen spores in the soils planted with wild oat was significantly lower than other crop soils. These results suggested that the wild oat soils had a greater degree of soil fungistasis. These may be one of the reasons why the BSR was suppressed by the wild oat. In the final year (2000), the suppressive effect by wild oat was checked in the farmer fields naturally infested with BSR pathogens. In the farmer fiels, the disease decreased dramatically and the yields was higher than that of other plots. From these three years results, the wild oat is best cleaning crops against the BSR disease and in near future oat will be combined among the cropping system in adzuki bean fields.