Powders of kudzu, velvetbean, and pine bark added to soil increase microbial population and reduce Southern blight of soybean

Southern blight (Sclerotium rolfsii) of soybean (Glycine max) is an important disease throughout the world. Some soil amendments can reduce disease levels by improving soil microbial activity. The main goals of this study were to investigate the effects of soil amendments such as dried powders of kudzu (Pueraria lobata), velvetbean (Mucuna deeringiana), and pine bark (Pinus taeda), on soil microbial population and disease caused by S. rolfsii on soybean. Pine bark, velvetbean (mucuna) and kudzu (25 g kg-1) added to soil were effective in reducing disease incidence [non-amended (NA) ~ 39%; amended (A) ~ 2 to 11%)]. Bacillus megaterium was the bacteria most frequently isolated in soils with velvetbean or kudzu (NA ~ log 5.7 CFU g-1 of dried soil; A ~ log 6.2). Soils with velvetbean and kudzu stimulated increase in population of Enterobacter aerogenes (NA ~ log 3; A ~ log 5.1-5.8). Pseudomonas putida population was higher in A than in NA (NA ~ log 4; A ~ log 5.5), and was negatively correlated (r = -0.83, P = 1%) to disease incidence. Soil amended with kudzu and pine bark stimulated increases in populations of Trichoderma koningii (NA ~ log 1.6; A ~ log 2.9) and Penicillium citreonigrum (NA ~ log 1.3; A ~ log 2.6), respectively. Penicillium herquei soil population increased with addition of kudzu (NA ~ log 1.2; A, ~ log 2.5). These microorganisms are antagonists of soil-borne pathogens. Powders of velvetbean, kudzu, and pine bark can increase antagonistic population in soil and reduce disease. A murcha (Sclerotium rolfsii) da soja (Glycine max) é uma doença mundialmente importante. Alguns resíduos orgânicos quando adicionados ao solo podem reduzir a doença devido ao aumento da atividade microbiana. Neste estudo investigaram-se os efeitos de pós-secos de kudzu (Pueraria lobata), mucuna (Mucuna deeringiana) e casca de pinus (Pinus taeda) adicionados ao solo, na população de microrganismos e na doença em soja. Casca de pinus (CP), mucuna e kudzu (25 g kg-1) incorporados ao solo reduziram a incidência de doença [sem aditivos (SA) ~ 39%; com aditivos (CA) ~ 2 a 11%)]. Bacillus megaterium foi freqüentemente isolada em solo com mucuna ou kudzu (SA ~ log 5,7 UFC g-1 de solo seco; CA ~ log 6,2).Solos com mucuna e kudzu aumentaram a população de Enterobacter aerogenes (SA ~ log 3; CA ~ log 5,1-5,8). A população de Pseudomonas putida foi maior em solos CA do que em solos SA (SA ~ log 4; CA ~ log 5,5). Houve correlação negativa (r = -0,83; P = 0,01) entre a quantidade de