[in Japanese]

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[in Japanese]

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[in Japanese]

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The importance of studies on soil animals as a tool to understand the dynamics of microorganisms in soil environment is reviewed. Soil animals are consisted of wide taxonomic groups, and are generally smaller than aboveground animals. Animal body and gut act as dispersal gear for soil microbes. Feeding of microorganisms reduce biomass, whereas physical and chemical defenses by microorganisms are well developed. Selective grazing by animals changes species composition of microbes. Animal guts provide specific microenvironment for microbes, hence it changes nutrient cycling. Microbes are mixed with water and nutrient in the earthworm gut thus gut environment becomes anaerobic, which is related to denitrification in the worm gut Worm casts are water stable aggregates, which changes soil functioning. Modification of soil structure by animals also has strong implication to microbial activities. Adopting conservation agriculture probably increases diversity and biomass of soil animals, therefore the studies on interaction between soil animals and microorganisms will become more important

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[in Japanese]

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The effect of Pratylenchus penetrans on the severity of Verticillium wilt in cabbage was investigated. First, the severity of the disease in cabbages grown in sterilized soils containing different concentrations of microsclerotia of V. longisporum or V. dahliae with or without P. penetrans inoculation was evaluated. The disease in soil containing 100 microsclerotia of V. longisporum/g dry soil with P. penetrans was significantly more severe than that in soil without inoculation of the nematode species, whereas there was no significant difference in disease severity between soils with and without P. penetrans in the presence of 1, 10, or 1000 microsclerotia of the fungus/g dry soil. Similarly, in soil harboring 1000 microsclerotia of V. dahliae/g dry soil, the severity was significantly increased by inoculation of P. penetrans in soil. Further, when cabbages were grown in sterilized soils containing 10 or 100 microsclerotia of V. longisporum /g dry soil inoculated with P. penetrans at different concentrations, disease severity in soil with 100 microsclerotia/g dry soil inoculated with higher concentrations of P. penetrans was greater than that in soil with lower concentrations of the nematode species, although there were no significant differences in the severity among soils with 10 microsclerotia/g dry soil inoculated with any concentration of P. penetrans. An increase in disease severity in cabbages by inoculation with P. penetrans in V. longisporum- infested soils was confirmed in a field experiment Thus, these results indicate that P. penetrans enhances the severity of Verticillium wilt in cabbage.

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