Genetic Variability and Symbiotic Efficiency of Erythrina velutina Willd. Root Nodule Bacteria from the Semi-Arid Region in Northeastern Brazil oleh Kelly Alexsandra Souza Menezes, Indra Elena Costa Escobar, Ana Carla Resende Fraiz, Lindete Míria Vieira Martins, Paulo Ivan Fernandes Júnior