The aim of this work was to isolate and to quantify diazotrophic bacteria associated with rice root, and evaluate their acid indolacetic production and their potential for biological nitrogen fixation, with the purpose of selecion promissing isolates for plant inoculation. N-fixing bactéria, settlers of the root interior of rice cultivars used in Rio Grande do Sul, Brazil, were isolated and quantified in nine cultivars. Rice root superficialy sterilized were macerated and introduced in specific culture media. Among 58 isolates obtained in the culture media NFB, LGI and LGI-P, the following were selected: UFSM-BD-02-06, UFSM-BD-08-06, UFSM-BD-14-06, UFSM-BD-20-06, UFSM-BD-26-06, UFSM-BD-31-06, UFSM-BD-36-06, UFSM-BD-42-06, UFSM-BD-48-06, UFSM-BD-54-06. The biological nitrogen fixation was determined by the Kjeldahl method, and indolacetic acid production by colorimetry. Azospirillum brasilense e A. lipoferum present greater values, 41.08 and 46.82 µg N mL-1, respectively, for total N, and for indolacetic acid production, A. brasilense, 41.09 µg mL-1, and UFSM-BD-31-06, 13.47 µg mL-1, are the greatest producers.
auxin; biological nitrogen fixation; isolation; rice root
