Microbes and Nematodes Associated with Rhizoplane and Rhizosphere Soil of Resistant and Susceptible Soybean Genotypes Grown in a Macrophomina phaseolina -Infested Field

Charcoal rot (CR), caused by the soilborne fungus Macrophomina phaseolina (MP), is a major disease of soybean [Glycine max (L.) Merr.] that leads to substantial yield losses. The uses of fungicides, cultural practices and biocontrol agents for CR management have not been widely adopted because of their limited successes. With the increase in production acreage and soybean monoculture, CR has continued to cause losses because there are no commercially available resistant soybean genotypes with complete resistance. Some soybean genotypes exhibit moderate resistance (MR) to CR, but the mechanism of this resistance is not completely understood. The MR soybean genotypes may be improved by implementing integrated agricultural practices that enhance microbial activity to suppress MP. The objective of this study was to investigate the effects of MR and susceptible (S) soybean genotypes on CR severity, bacterial and nematode community structures, and soil fertility in a MP-infested field. We found that CR severity was consistently lower in MR genotypes. Most soil chemical properties and soil organisms were not affected by CR resistant genotypes. However, a few bacterial taxa and nematode trophic groups with known associations with enhanced plant disease resistance were negatively associated with disease severity in MR genotypes. Hence, using MR soybean genotypes and adopting agricultural practices that support plant growth promoting bacteria and fungivore and omnivore nematodes could reduce CR severity.