Strains of Bradyrhizobium spp. in the biological control of phytopathogens in the soybean

Abstract

Bacteria of genus Bradyrhisobium form a symbiotic relationship with legumes, promoting biological nitrogen fixation (BNF). However, their effect on the biological control of disease has not been investigated. The aim of this study was to evaluate the effect of four strains of Bradyrhisobium spp., namely SEMIA 5080, SEMIA 5079, SEMIA 5019 and SEMIA 587, on the in-vitro control of four soil phytopathogens: Fusarium crassistipitatum, Macrophomina phaseolina, Rhisoctonia solani and Sclerotinia sclerotiorum, which cause root rot in the soybean. All the strains of Bradyrhisobium spp. and of the phytopathogens were obtained from Embrapa Soja in Londrina, Paraná. In-vitro tests were conducted using the circle method (adapted), and comparing soybean seeds inoculated with the bacteria and the phytopathogens. The dishes subjected to the circle test were evaluated using a scanning electron microscope (SEM). Two tests of antibiosis were conducted using filtrates of metabolites from Bradyrhisobium spp.: assessment of the minimum inhibitory concentration (MIC) and of the antibiosis in Petri^® dishes. The results were submitted to the Lilliefors test of normality, followed by ANOVA and regression analysis using the Genes software. The comparison showed that the SEMIA 5080 and SEMIA 5019 strains achieved the best control of the four phytopathogens, with a good performance by the SEMIA 5079 strain; however, the SEMIA 587 strain showed no control over the pathogens. There was morphological damage to the hyphae of each of the phytopathogens subjected to the circle method. There was no antibiosis from the filtered or volatile metabolites.