Potencial antagonista de bradyrhizobium spp. sobre patógenos de solo da cultura da soja

Abstract

Bradyrhizobiumspp., it is characterized as a good inoculant for biological nitrogen fixation in soybean, but its potential in the control of phytopathogens is still little known. Thus, the present work aims to evaluate the potential antagonist of four strains Bradyrhizobium spp. SEMIA 587, SEMIA 5019, SEMIA 5079 and SEMIA 5080 in the biological control of Fusarium crassistipitatum, Macrophomina phaseolina, Rhizoctonia solani,and Sclerotinia sclerotiorum.The in vitro experiment was evaluated or antagonized by Bradyrhizobium spp. through direct confrontation involving two methods, the method of confrontation with the biological control agent versus the adjustment in the culture medium, which consists of Petriplates with YM medium, where the strains of Bradyrhizobium spp. they were placed in a 4 cm diameter circle, and no center of this circle was transferred to a 7 mm diameter mycelium disk of the phytopathogenic fungus; and by the soybean seed microbiolization method with strains of Bradyrhizobium spp., where microbiolized seeds were placed 1 cm away from the edge of the Petriplate with BDA medium, and on the opposite side was transferred to a 7mm mycelium disk adjustment diameter 1 cm away from the opposite edge. As the samples of each treatment of the confrontation method in the culture medium were subjected to scanning electron microscopy with 500 times magnification, an end of observation as morphological changes of the fungal hyphae when in direct contact with the studied cephae. Assays were also performed to verify the antibiosis of Bradyrhizobiumspp. Strains using the cell-free agent filtrate, which was incorporated into 10% concentration BDA flux media and transferred to Petriplates in the center of the plate, a 7mm diameter mycelium disc of the pathogen was arranged according to treatments. The Minimum Inhibitory Concentration (MIC) methodology was used for the verification of antibiosis through serial microdilution of Bradyrhizobium spp. free fromliving cells. For both confrontation methods and plaque antibiosis evaluation, mycelial growth evaluations were performed daily with the aid of a graduated ruler every 24 hours until the control containing only the phytopathogen reached full growth at theedge of the plate. Petriplate. The experimental design adopted in all experiments was completely randomized with four replications. The obtained data were submitted to the Lilliefors normality test; and because these were qualitative x quantitative experiments, ANOVA was performed followed by regression analysis in the Genes software. It can be observed in the confrontation by both the adapted method ofthe circle and the microbiolization of soybean seeds that the SEMIA 5080 and SEMIA 5019 strains obtained the best control of the four studied phytopathogens, followed by the good performance of the SEMIA 5079 strain. The SEMIA 587 strain showed no controlover phytopathogens. The strains of Bradyrhizobium spp. showed no antibiosis on phytopathogens at 10% concentration, as well as on MIC.