We developed a microbial inoculum (Material A) which contains 5 Actinomycetes isolates antagonistic against Fusarium oxysporum with an organic career. The career material was able to promote the activity of Actinomycetes in soil (Soil Microorganisms 38: 41-48, 1992). In the present paper, the effects of the inoculum (Material A) on the soil microbial flora were investigated in relation to soil environmental conditions such as pH (pH 5.3, 7.0, and 7.8), moisture level (MWHC 20-80 %), and temperature (20, 30, and 40℃). The application of the inoculum resulted in a high population density of Actinomycetes in soil irrespective of environmental factors, unless the soil moisture level was very low (20 % MWHC). An effective method of application was also examined for controlling radish yellows caused by Fusarium oxysporum f. sp. raphani. When radish plants were grown in soil infested with the pathogen, amendment of soil with the inoculum (Material A) decreased the disease severity. Especially, when the inoculum was applied to sterilized soil one week before the introduction of the pathogen and one or two weeks before the seeding of radish plants, the disease was almost completely suppressed. Continuous application of the inoculum (Matrial A) as well as that of crab shell seemed to promote the suppressive effect against the disease. The present results suggest that the microbial inoculum (Material A) suppressed radish yellows under various soil conditions and its effectiveness may be enhanced by the improvement of the method of application to soil.
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