In tropical legumes, a careful selection of rhizobia strains, among other factors, is essential for the efficiency of biological nitrogen fixation (BNF). This selection should be made for leguminous crops of social and economic interest, such as lima bean (Phaseolus lunatus L.). The aim of this study was to evaluate the symbiotic effectiveness of rhizobia from two regions of Piauí producing lima bean. Seventeen isolates and two reference strains CIAT 899 and NGR 234 were evaluated on the fava bean genotype "UFPI-468". The study was conducted in a greenhouse in autoclaved Leonard jars, in a randomized block design with three replications. Inoculation was done at planting. Samples were collected 34 days after planting to assess the following variables: shoot dry mass (SDM), root (MRS) and nodules (MNS), ratio SDM/MRS, accumulated nitrogen (Nac) in SDM by the Kjeldahl method, and N2-fixation efficiency. Significant interactions were observed among all variables except for MSR. In general, the values for DMAP, MRS , DMAP/MRS, Nac and N2-fixation efficiency of the isolates ISO-18, ISO-23, ISO-24, ISO-25, ISO-30, ISO-32, ISO-35, ISO-36, ISO-43, and ISO-45 were higher than of ISO-2, ISO-9, ISO 16, and ISO-40 and the absolute control. The variables used in this study were sufficient to discriminate and select nodulation-efficient strains for lima bean, increasing the effectiveness of BNF. Most isolates performed well in terms of N supply to plants and can be recommended for tests of agronomic efficiency.
biological nitrogen fixation; nodulation; symbiosis; Bradyrhizobium sp
