Rhizobia isolation and selection for serradella (Ornithopus micranthus) in Southern Brazil

ability to associate symbiotically with rhizobia. The objective of this study was to isolate, authenticate and select effective rhizobia obtained from native serradella (Ornithopus micranthus) to reduce the need for mineral fertilizer. Nodules, roots of serradella and rhizosphere soil samples were collected in seven municipalities from Rio Grande do Sul and Santa Catarina states. Bacterial colonies were isolated and identified based on morphological characteristics. The authentification and initial selection of rhizobia were conducted in vitro. The most promising strains from the in vitro study were evaluated in a greenhouse experiment for 60 days. Among the 148 bacterial cultures characterized, 113 induced the formation of nodules in serradella while 32 isolate effectively increased fresh mass of plants under in vitro conditions. The strains UFRGS Om57, UFRGS Om59 and UFRGS Om148 formed nodules with greater dry mass and produced high dry mass of plants (shoots and roots) which allowed greater accumulation of N in the shoots. Key words: Plant growth promoting rhizobacteria (PGPR); biological fixation of nitrogen; Ornithopus micrantus; pasture.