Características simbióticas e fenotípicas de Azorhizobium doebereinerae, microissimbiote de Sesbania virgata

Abstract

Four experiments were carried out under greenhouse conditions. The first and second experiments aimed to evaluate the nodulation capability and symbiotic efficiency of S. virgata (N2 fixation) with homologous rhizobia strains (isolated from nodules of the same species after inoculation with soil samples from the Amazon forest or from southeastern Brazil, and identified as Azorhizobium doebereinerae) and with rhizobia strains isolated from nodules of other leguminous species. The third and fourth experiments aimed to verify whether the presence of A. doebereinerae in soils of different ecosystems of two municipalities in southern Minas Gerais is related with the occurrence of S. virgata. The four experiments comprised treatments inoculating different strains (experiments I and II) or inoculating soil suspensions of composed samples collected from different ecosystems of southern Minas Gerais, including areas where S. virgata occurred (experiments III and IV). All the experiments had three control treatments to verify the absence of contamination and suitability of experimental conditions for symbiotic efficiency expression, besides being references for comparison of the other treatments. Two control treatments were without inoculation, with and without mineral nitrogen (35 mg.L-1 N- NH4 NO3). The third control treatment was inoculated with strain BR 5401T, recommended as inoculant for S. virgata and also the type strain A. doebereinerae. Treatments were applied to previously germinated seeds transferred to dark glass vials with 800 mL of nutrient solution without nitrogen, where plants where allowed to grow during 50 days. In the first and second experiments it was verified that S. virgata only nodulated when inoculated with homologous rhizobia strains, i.e., strains isolated from nodules of the same species. In the third and fourth experiments, it was verified that S. virgata would nodulate only when inoculated with soil samples collected close to S. virgata plants. It was concluded that A. doebereinerae isolates from the Amazonia and Minas Gerais soils presented high phenotypic and symbiotic similarity among them and BR 5401T and that S. virgata and A. doebereinerae symbiosis is highly specific and efficient for all strains.