Isolamento e seleção bactérias diazotróficas em cultivares de arroz recomendadas para o plantio no Estado do Rio de Janeiro

Abstract

Rice (Oryza sativa L.) is one of the main foods of the world population that provide most of the protein and caloric needs of human beings. Rice cultivation in the State of Rio de Janeiro has undergone profound changes which resulted in a decrease in planted area and consequent production loss. In the 60’s, the cultivated area in Rio de Janeiro State reached more than 80 thousand hectares, but nowadays cultivation area is just of 1.4 thousand hectares, producing about of 4.3 tons of grains corresponding to less than 1 % of the national crop. To reduce production costs and increase the productivity of rice in the Rio de Janeiro State some alternatives have been studied. In this context, this work aimed to isolate, characterize and select diazotrophic bacteria of the genus Azospirillum and Herbaspirillum, associated with rice cultivars recommended for cropping in the Rio de Janeiro State and to evaluate their inoculation effects. A total of 39 diazotrophic bacteria isolates associated with BRS TROPICAL and EPAGRI TROPICAL-109 were obtained. Then 18 isolates were selected based on results of acetylene reduction assay (ARA), indolic compounds production, phosphate solubilization and siderophores production. Among them there were found isolates belonging to the genera Azospirillum, Herbaspirillum, Paenibacillus, Ideonella and Pseudomonas. The isolates that showed in vitro the best plant growth promotion (PCP) characteristics were used in experiments at gnotobiotic condition and in greenhouse. The most efficient strains used in gnotobiotic condition promoted increments up to 31% on the dry mass of plants due to inoculation. Based on the data of this experiment there were selected two promising isolates to evaluate in greenhouse experiments, using some reference strains as standard. The greenhouse experiment treatments consisted of inoculation, nitrogen fertilizer doses (N) (30, 60, 90 e 120 kg de N ha-1) and cultivars EPAGRI-109 and BRS TROPICAL. The inoculation treatments with strain EP4-1L of A. amazonense, the commercial inoculant AZOTOTAL and the A. brasilense standard strain Sp245 showed significant increase of the production of panicles in EPAGRI-109 rice variety in 19.8%, 23.9% and 39.9%, respectively, at a dose of 30 kg N ha-1.