Microbial communities in soils with different population densities of soybean cyst nematode

The relationship of abiotic factors with soybean cyst nematode (SCN), the most damaging pathogen of soybean, has been studied extensively, but characterization of microbial communities in infested soils and on soybean roots under field conditions remains unknown. This study investigated the relationship of different SCN population density levels with soil physical, chemical and microbial properties in soils and on soybean roots. A commercial soybean field with different levels of SCN densities (low, medium, high) was sampled, and microbial communities were characterized using both dilution plating assays and molecular approaches. Population densities of species of Trichoderma, actinomycetes, Pseudomonas and other bacteria were significantly higher (P0.05) in soils with low SCN (SCN-C) compared with high (SCN-A) and medium levels (SCN-B). Diversity indices of Trichoderma communities on roots based on denaturing gradient gel electrophoresis (DGGE) were significantly higher in soils with SCN-C compared with SCN-A and SCN-B. Cluster analyses and canonical correspondence analysis (CCA) generally separated microbial communities into three groups based on different SCN levels, and CCA showed that low SCN population levels were positively correlated with high levels of nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), cation exchange capacity (CEC), base saturation (BS), the populations of Trichoderma and bacteria. Moreover, diverse Trichoderma, Pseudomonas, Bacillus and actinomycetes were found on roots in SCN-C soils based on dilution plating and DGGE, suggesting that the presence of these microbes on soybean roots might be associated with improved plant health and reduction of SCN.