Biological Nitrogen Fixation Stability of Cowpea Cultivars With Tropical Semi-Arid Rhizobial Strains

Abstract

Cowpeas (Vigna unguiculata L. Walp) are an economically and socially important legume in northern and north-eastern Brazil and can establish effective symbiosis with nitrogen-fixing bacteria. We evaluated the symbiotic compatibility and efficiency of rhizobial strains from Pernambuco semi-arid soils and determined their symbiotic stability on the IPA-206, BR 17-Gurguéia, and BRS Novaera cultivars, selected for different environments. The experiment was conducted in a greenhouse to evaluate a 3 × 28 factorial arrangement (cultivars selected for different environments × inoculation with the currently recommended strain, uninoculated plants with or without mineral nitrogen, and 25 rhizobial strains from semi-arid soils) in a randomized block design with four replicates. We determined nodule number, shoot and root dry matter, nodule dry matter by nodule number, nitrogen accumulated in the shoot by nodule dry matter, nitrogen content and accumulation in the shoot, relative efficiency of the recommended strain based on nitrogen accumulation, and shoot dry matter. Overall, the cultivars responded differently to different strains and cultivar biological nitrogen fixation potential. Strains G7.85 and BR 3262 showed potential for biological nitrogen fixation. BR 3262 was confirmed to be adequate for inoculation of different cowpea cultivars.

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“…Concerning cowpea, four strains are recommended: BR 3267 identified as Bradyrhizobium yuanmingense [ 70 ]; BR 3262 identified as Bradyrhizobium pachyrhizi [ 70 ]; UFLA 03–84 identified as Bradyrhizobium viridifuturi [ 71 ]; and INPA 3-11B identified as Bradyrhizobium elkanii [ 72 ]. Inoculation with these strains may significantly increase BNF contributions from 36 to 75 kg N ha −1 [ 69 , 73 , 74 ]. In Venezuela, Artigas Ramirez et al [ 75 ] found that rhizobia nodulating cowpea are mainly fast growing, including the genera Rhizobium and Ensifer, and the β-rhizobia genera Burkholderia and Paraburkholderia, although Bradyrhizobium has also been found.…”