Abstract
The present investigation was undertaken to demonstrate the relationship between soft-rot bacteria (Erwinia sp.) and soil structure. The distributions actinomycetes, and fungi within soil aggregates were examined by the serial washing and sonic vibration method designed by Hattori. Microbial cells in the aggregates were thus fractionated into those in inner and outer parts.
1. It was found that the number of soft-rot bacteria in individual fractions of aggregates isolated from the soil in contact with midribs of chinese cabbage in late stages of its wrapping, designated as phyllosphere soil, was almost equal. On the contrary, the numbers of other organisms increased up to 150 percent with the decrease in the size of aggregates of the fractions.
2. When these fractions of aggregates were exposed to sonic treatment for three minutes, an increase in the numbers of microorganisms with the exception of soft-rot bacteria was observed.
3. Soft-rot bacteria were detected by dilution plating in 29 of 46 soil aggregates, their numbers ranging from 12 to 1, 600. There was no correlation between the numbers of soft-rot bacteria and of dye-tolerant bacteria in individual soil aggregates (2.00-0.84mm).
4. It was found that 90 percent or more cells of soft-rot bacteria resided in the outer part of soil aggregates collected from the rhizosphere and phyllosphere of chinese cabbage.
5. The rhizosphere effect of chinese cabbage on bacterial flora in the soil aggregates was more pronounced in the outer part than in the inner part.
