Rhizobia Strain Selection and Symbiotic Compatibility with Different Cultivars of Cowpea (Vigna unguiculata (L.) Walp) in Brazil.

Cowpea [Vigna unguiculata (L.) Walp] may be cultivated under adverse soil and climate conditions, and may nodulate and fix nitrogen with a wide range of rhizobia. A continual search for new bacterial strains is important to select more efficient and adaptable associations, and a better evaluation of symbiotic stability may contribute to strain recommendation. The symbiotic compatibility and efficiency of strains from soils of the semiarid region of Pernambuco, and the recommended strain BR 3262, and their symbiotic stability with BR 17-Gurguéia, IPA 206 and BRS Novaera cultivars was estimated. A greenhouse experiment was conducted with these cultivars, 25 isolates, the recommended strain and uninoculated treatments with and without N. Shoot, root and nodule dry matters, nodule number, specific nodule mass, shoot N by nodule dry mass unit, and relative efficiency of inoculated strains in relation to the currently recommended strain were determined. Sixteen isolates nodulated had as much as BR 3262, while for specific nodule mass 20 isolates did not differ from BR 3262, and 18 for shoot nitrogen per each nodule dry matter mg. Strain by cultivar interactions were observed for relative efficiency estimates on a shoot dry matter and fixed nitrogen basis, indicating potential for selection of more efficient symbiotic pairs. The strains with improved stability and adaptability to cultivar with high potential for biological nitrogen fixation are G7.85 and BR 3262.