Seleção de estirpes de rizóbio, actinobactéria e bacillus para coinoculação em feijão-caupi

Abstract

In Brazil, beans are one of the main components of the population's diet, widely consumed due to their low cost and high nutrient content, contributing to food and nutritional security. The most commonly consumed types of beans in the country are common beans (Phaseolus vulgaris) and cowpeas (Vigna unguiculata). In this context, the use of bio- inputs based on plant growth-promoting microorganisms stands out as a promising strategy for reducing costs and environmental impacts and improving food quality. Biological nitrogen fixation (BNF) plays a key role in the biogeochemical cycle of nitrogen and promotes increased soil fertility. Given this, the present study aims to select strains of rhizobia, actinobacteria, and Bacillus spp. for co-inoculation to promote the growth of cowpea. The experiments were conducted in a greenhouse, and a two-stage screening was performed to select the rhizobium strains with the best symbiotic performance from a total of 58 strains. Subsequently, the selected rhizobium strains were characterized by genome sequencing. Co-inoculation trials were conducted using rhizobia in association with 21 strains of actinobacteria and seven strains of Bacillus spp. The dry biomass of the aerial parts, roots, nodules (g per plant), and nitrogen accumulation in the aerial parts (mg per plant) were evaluated. Growth promotion mechanisms such as indoleacetic acid (IAA) production, siderophores, biosurfactants, phosphorus solubilization and mineralization, and free-living nitrogen fixation capacity were evaluated. Three rhizobium strains promoted dry biomass accumulation higher than the non-inoculated treatment in both selection phases and were classified based on their genome as belonging to the genus Bradyrhizobium. No statistically significant differences were observed between treatments in the two experiments of co-inoculation of rhizobia with actinobacteria and Bacillus spp. Bradyrhizobium spp. strains showed high biosurfactant production capacity, actinobacteria strains showed high phosphate solubilization and mineralization capacity, and Bacillus spp. strains showed high AIA production capacity. Thus, the selection of multifunctional plant growth-promoting bacteria and the composition of bacterial consortia are efficient and sustainable strategies for promoting productivity, quality, and cost reduction in cowpea.