Evaluation of diazotrophic bacteria from rice varieties (Oryza sativa L.) grown in Rio de Janeiro State, Brazil

The indiscriminate application of nitrogen fertilizer in order to increase rice crop productivity contributes to environmental degradation. One of the possible alternatives to ease up this problem is the use of sustainable and cost-effective technologies such as biofertilizers to promote plant growth. This work aimed to isolate, characterize and select diazotrophic bacteria associated with rice cultivars EPAGRI-109 and BRS TROPICAL. About 39 bacteria belonging to the genera Azospirillum, Herbaspirillum, Paenibacillus, Ideonella and Pseudomonas were isolated. Based on the best results of acetylene reduction assay (ARA), indolic compounds production and phosphate solubilization, the isolates were selected as potential plant growth promoters which were tested on rice cultivars IR 42, EPAGRI 109 and BRS TROPICAL under axenic condition and the most efficient isolates promoted up to 31% of dry weight of the evaluated rice cultivars. Two promising isolates were selected in this work (Paenibacillus species strain EP3-16N and Nitrospirillum species strain EP4-1L), however, more studies are necessary to confirm this capacity in field conditions. Key words: Plant growth promoters, biological nitrogen fixation, rice cultivars.