Interação planta-bactéria diazotrófica na cultura do arroz

Abstract

The inoculation of rice plants with diazotrophic bacteria is an alternative for reductio n of usage of nitrogen fertilizers in the crop. However alterations in the plants development are observed in this type of association. The present study had as objective to evaluate the influence of bacteria inoculation in development of rice cultiva rs, through agronomic and physiological parameters. To evaluate the effect of diazotrophic bacteria inoculation in development of rice plants in different handling forms, an experiment of inoculation in laboratory and three experiments in green - house were conducted. The first experiment was carried through with rice plants growing in tubes with nutrient solution; the second, in cups filled with sand; and the third and fourth, in vases with soil. In all experiments, there were used lineages of Herbaspirillum seropedicae (BR11417 - ZAE94; BR11507 - M2), Burkholderia spp (BR11340 - M130) and Azospirillum brasilense (BR11002 - Cd), inoculated individually, or using mixes of two or more lineages. The acid production of indol acetic (AIA), and acetylene reduction activity (ARA) of diazotrophic bacteria lineages also were evaluated, without plants, only in culture media. The results demonstrated that all lineages were able to produce AIA in the presence of triptophane; having the lineage Cd presented the biggest concentrations. With exception of the M2 lineage, all had ARA in the culture media. However, with the evaluated parameters, it was not possible to correlate AIA production AIA and the lineages ARA, with promotion of vegetal growth. The experiments in laboratory and green - house, using the rice cultivars IR42 and IAC4440, demonstrated that application of a nitrogen fertilizer dosage of 50kg N ha-1 allowed better interaction between rice plants and diazotrophic bacteria. The rice cultivars IR42 and IAC4440 responded differently to inoculation with diazotrophic bacteria, which was related to the cultivation environment. The inoculation of lineages of diazotrophic bacteria propitiated a highest N level and bulk grain protein of IR42 cultivar, without causing a reduction in its productivity. In the fourth experiment, there were observed, as a function of inoculation, variations in activity of nitrate reductase enzyme and partition of soluble fractions (nitrate, amino acids and soluble carbohydrates) during the vegetative cycle. However, a relationship between these physiological parameters and the production of rice cultivars was not observed.