Processos promotores de crescimento vegetal por bactérias diazotróficas de vida livre ou simbióticas de feijão comum, Caupi e siratro

Abstract

Soil environment is complex , heterougenous and dynamic. It harbors several processes mediated by microorganisms which can contribute to enhance plant growth. These processes are mediated by bacteria named plant growth promoting rhizobacteria (PGPR) which live in the rhizosphere. Among processes mediated by PGPR , some act direct on plant growth promotion, by producing specific compounds or enhancing nutrient absorption by roots, like nitrogen fixation, phosphate solubilization or growth hormones Biological nitrogen fixation is the plant growth promoting process most studied among associative and endophytic bactéria. It is well know the significant contribution of nodulating bacteria for Leguminosae nutrition. By excreting organic acids as well as by other mecanisms bacteria solubilize inorganic phosphate liberating phosphorus for the plant and other organisms. Plant growth promoting hormones are natural regulators that, in low concentrations, can influence physiological processes, hence controlling plant growth. Bacteria can also contribute indirectly for plant growth, decreasing or preventing deleterious effects of phytophatogenic microrganisms. The ability of bactéria to mediate these processes in the rhizosphere can contribute for increasing the effect of inoculants with greater benefits for farmers, decreasing the amount of chemical fertilizers applied and promoting yields increase with low costs. Furthermore, there is the possibility of using these bacteria both in legume and non legumes.