To examine the differences in nematode survival in soil microhabitats, second stage juveniles (J2) of M. incognita were hatched directly in an andosol from buried egg-masses or inoculated to the soil soon after hatching in water. The soil was adjusted to a moisture content of pF2 and stored at 25℃. After a certain period of time, the J2 in the soil were extracted from soil aggregates larger than 0.25 mm in diameter, or outside of them by using a combination of sieves with 0.25 mm, 1.0 mm, 2.0 mm and 4.0 mm apertures and the double layer centrifugal flotation extraction method. The J2 extracted from soil aggregates smaller than 0.25 mm in diameter were considered to have survived outside of the soil aggregates while those extracted from soil aggregates larger than 0.25mm in diameter were considered to have survived inside of the soil aggregates. From the beginning of storage, the proportions of J2 extracted from inside of the soil aggregates were higher for the J2 hatched directly in soil than for those hatched in water and inoculated there after. Survival rates were higher in the former J2 also. In both types of J2, some of them tended to migrate gradually into soil aggregates during the periods of storage. The J2 in soil aggregates survived for more than 30 days retaining a large amount of food reserves, though those remaining outside of the soil aggregates consumed food reserves rapidly and died soon.

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Differences in survival time of second stage juveniles (J 2) of M. incognita were examined in an andosol that was sieved to obtain soils with aggregates smaller than 0.25 mm, 0.25-1 mm, 1-4 mm, or 0-4 mm in diameter. The soil consisting of 0-4 mm aggregates had a range of aggregates in the same proportion as that of the original soil. The J 2 were hatched from egg-masses buried in soils differing in aggregate composition. After four days, the egg-masses were removed and the soils were stored in moist chambers at 25℃. After 0, 5, 10, 30 and 60 days of storage, the J 2 were extracted from inside or out side of soil aggregates by using a combination of sieving and double layer centrifugal flotation extraction method. The ability of the J 2 to migrate through a 1 cm sand column and the amount of food reserves present were used as indicators to evaluate the survival ability. The J 2 survived longer in soil with aggregates with a larger diameter than in soil with aggregates with a smaller diameter. In particular, most of the J 2 in soil with aggregates smaller than 0.25 mm in diameter died within 30 days due to the small amount of available food reserves. The J 2 associated with the larger soil aggregates survived for more than 60 days and retained a large amount of food reserves. The results suggest that long term survival of M. incognita J 2 in soil depends on the penetration of them into, or their association, with large soil aggregates. The large aggregates seem to contribute to the preservation of food reserves by reducing J 2 movement in soil.

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Effect of a microbial inoculum (Material A) which contains 5 strains of antagonistic Actinomycetes against Fusarium oxysporum with an organic carrier on the control of Fusarium diseases was investigated in pot, frame plot and field experiments. Material A suppressed radish yellows in pot and frame experiments using infected field soils and affected the population density of F. oxysporum in radish roots and rhizosphere soils. In the field experiments, radish yellows and Fusarium wilt of strawberry were also suppressed by the application of Material A. The suppressive effect of Material A on Fusarium diseases was more pronounced in stripe application than in broadcasting application. Co-application with chlorpicrine was the most effective way of using Material A for tfe control of Fusarium diseases. The control effect of Material A on Fusarium diseases was influenced by the application of a large amount of other organic materials, such as bark compost, cow compost or pig compost. In many cases, Material A was effective in the control of Fusarium diseases such as radish yellows and Fusarium wilt of strawberry. Control of the diseases using this material may be successful when it is combined with the application of other chemicals.

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Mechanisms of control of radish yellows by using a microbial inoculum (Material A) which contains antagonistic Actinomycetes against Fusarium oxysporum f. sp. raphani with an organic carrier were investigated. First, a method for determining the chlamydospore density of F. oxysporum in soil was newly developed to enable a more accurate determination of the chlamydospore density in soil. Secondly, the effect of Material A on the control of radish yellows was examined in pot experiments. The suppressive effect of Material A varied with the time of application and sowing. Material A did not exert a significant effect on the total Fusarium density but increased the density of the chlamydospores in soil. The disease was well controlled in the soil where the density of chlamydospores was high and that of infection forms, mycelia and conidia, of the fungus was low at the time of sowing. Thirdly, the effect of Material A on F. oxysporum was examined in Petri dishes. Material A suppressed the germination of chlamydospores and subsequent hyphal growth, resulting in a high density of chlamydospores in soil. The results obtained suggest that the enhancement of soil fungistasis is one of the mechanisms of control of radish yellows by Material A.

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We have investigated the relationship between soil formation and development of bacterial communities in coastal sand dunes. Diversity of bacterial strains isolated from immature soils of vegetation series, i.e. bare land (Pd. 1, pd. 2 B) -grassland (Pd. 2)-woodland (Pd. 3 , pd. 4) along the sea shore was determined by examining the pattern of carbon source utilization. Patterns of utilization of sixty one different carbon sources were assigned a numerical value by using a binary number, 1 or 0 refering to the utilization or non-utilization. The isolates composing a community were clustered (UPGMA) according to the numerical characteristics. Diversity index was calculated by total aggregate distance within multidimensional space and average distance separating each component. The bacterial communities in the sandy soil of the grassland (Pd. 2) were much more diverse than those of the sand without vegetation (Pd. 1, pd. 2 B). Diversity of bacterial communities in the grassland (Pd. 2) was similar to that in an A horizon of woodland soil (Pd. 3, pd. 4). These results indicated that the bacterial communities become diversified in the area where vegetation appeares in the sand.

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[in Japanese]

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[in Japanese]

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Effect of Mn^<2+> on the growth and γ-HCH (γ-1, 2, 3, 4, 5, 6-hexachlorocyclohexane)-decomposing activity of a bacterium, Sphingomonas paucimobilis SS86, in liquid culture medium was examined to estimate the usefulness of Mn^<2+> as a regulator of microbial inocula in the environment. A low concentration (10 mg L^<-1>) of Mn^<2+> completely inhibited the growth of strain SS86 in diluted nutrient broth. The inhibitory effect of Mn^<2+> on the bacterial growth which was observed in a pH range of 6.0-7.5 was relatively weak under low pH (6.0) conditions. Gamma-HCH-decomposing activity of SS86 was also suppressed by Mn^<2+>, but the lowest inhibitory concentration of Mn^<2+> for the γ-HCH-decomposing activity was higher than that for bacterial growth. Mn^<2+> is considered to be an effective agent for the control of the growth and activity of bacterial inocula in the environment.

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