Erythrina velutina (“mulungu”) is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of “mulungu” rhizobia are poorly understood. The aim of this study was to characterize “mulungu” rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L⁻¹ of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

The inoculation of rhizobia in lima bean can increase its yield and contribute to smallholder farms. In this study, the potential of rhizobia in increasing the lima bean yield was evaluated in two regions from Piaui and Ceará states. The experiments were conducted in field comparing three rhizobia strains (UFPI32, UFPI38, UFPI59), one strain of reference to Phaseolus vulgaris (CIAT899) and two controls (with and without nitrogen). The parameters of nodulation, N accumulation and yield varied between treatments and locations. The nodule biomasses were higher in UFPI59 and UFPI32 (Piauí), and CIAT899 and UFPI32 (Ceará). The highest values of nodule size were found in treatments UFPI59 in both locations. Lima bean presented highest values of leaf N in UFPI59 and CIAT899. The highest values of grain yield were found in the treatment UFPI59 as compared to CIAT899 and the controls. The results confirmed the potential of UFPI59 in promoting nodulation, N accumulation, plant growth and yield of lima bean in both locations.