Abstract
To verify the relation between disease severity by Chinese cabbage yellows (Verticillium wilt, caused by Verticillium dahliae, V. longisporum and disease-promoting nematode Pratylenchus penetrans) and soil microbiota in fields, bulked soils were periodically sampled in fields with different severities in Gunma Prefecture. Shannon-Wiener diversity index (H') for bacteria, fungi and nematodes, as well as presence of the causal pathogens, were determined based on fingerprint patterns generated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Consequently, although the diversity indices of soil bacteria and fungi sampled after harvesting were not significantly correlated with the disease severities in fields the next year, H' for nematodes in the soil was highly negatively correlated with disease severity. Furthermore, the relative intensities of DGGE bands that represented the causal agents in the soils sampled after harvesting were positively correlated with disease severity, and those for P. penetrans were negatively correlated with H' of all nematodes in the soil microbiota. Thus, H' of the all nematodes and relative intensities of DGGE bands of the causal pathogens in the soils after harvesting in the previous year could serve as soil microbiological predictors correlating with disease severities in the fields in the succeeding year.
