A new antagonistic bacterium Bacillus sp. BS-1 from rhizobacterial isolates was selected in term of its suppressiveness against soil-borne plant pathogens (Noguchi 1992). In this paper we examined the characteristics of BS-1 and its effectiveness for suppression against soil-borne plant pathogens: 1) Physiological tests of Bacillus sp. BS-1 showed that BS-1 is a new species. 2) BS-1 was mutated with NTG, and a mutant BS-1 SMCP III resistant to chloramphenicbl was isolated. 3) To trace BS-1 SMCP III in soil-plant systems, a selective medium was developed by using pigments, antibiotics, buffer agents, inorganic bases and amino acids. 4) The growth characteristics of BS-1 on 24 kinds of different organic materials were examined and an organic material of animal origin to be a good substrate for BS-1. A microbial inoculum BS-1 containing it was developed. 5) The effectiveness of the microbial inoculum BS-1 on soil-borne plant pathogens was examined by using a mutant BS-1 SMCP III and its selective medium. The application of the inoculum BS-1 to the seeding bed or culture soil suppressed soil-borne diseases of tomato, cucumber and melon. Root surface of the plant and the soil to which the inoculum was applied were found to be colonized by BS-1 SMCP III.

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Basal rot of rakkyo (Allium chinense) is caused by Fusarium oxysporum f. sp. allii. Non-pathogenic strains of Fusarium moniliforme and Fusarium oxysporum were isolated from the healthy root tissues of rakkyo. Preinoculation treatment of rakkyo bulbs by dipping them in the bud-cell suspension of the non-pathogenic isolates reduced the disease incidence in the infested field. This method was more effective than soil drenching with a bud-cell suspension of isolates. However, the effect depended on the inoculum concentration. Preinoculation with a mixture of F. moniliforme and F. oxysporum led to a higher disease suppression than when the strains were used singly. The isolates of F. moniliforme and F. oxysporum were also non-pathogenic to other crops, viz., rice, tomato, eggplant, cucumber, melon, watermelon and radish.

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Effects of biodegradable urea condensation polymer (urea-polymer) on microorganisms and on soil microflora were examined. The 30 strains of microorganisms were classified bases on the utilization of urea-polymer as a sole nitrogen source. All of eight strains of PGPR, antagonistic bacteria and enterobacteria utilized the urea-polymer as a nitrogen source; out of 9 strains of soil bacteria and pathogenic soil bacteria, 4 strains utilized it which all of six actinomycetes did not utilize it. Out of seven strains of fungal plant pathogens, only one strain utilized the urea-polymer as a nitrogen source. In the lawn field 25 months after application of the urea-polymer, the numbers of thermotolerant spore formers, fluorescent Pseudomonads, actinomycetes and fungi in the soil were 61 times, 10 times, 4 times and 2 times higher than those in the control soil, respectively. In the rhizosphere soil and rhizoplane 75 days after application of the urea-polymer, the populations of thermotolerant spore formers and fluorescent Pseudomonads were higher than those of the control. Furthermore, the population ratio of specific prokaryotes to fungi (SP/F) was also higher in the urea-polymer treated soil. By application of the urea-polymer, the SP/F values of the rhizoplane changed markedly compared with those of the rhizosphere soil. Results of ELISA indicated that the population of P. cepacia increased in the rhizosphere soil by the application of the urea-polymer. These results suggest that the urea-polymer may act as a nitrogen source for antagonistic bacteria in a carbon-rich environment i.e. plant rhizosphere, and that it may change the microbial communities of the plant rhizosphere.

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Scab-inducing phytotoxin was isolated from the tissues of potato tubers and from oatmeal broth medium inoculated with Streptomyces turgidiscabies 91 SY-10 C strain. Spectroscopic analysis of the active compound gave sufficient information to identify this substance as thaxtomin A. A Study of 35 pathogenic S. turgidiscabies strains showed a positive correlation between their pathogenicity and thaxtomin production.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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