Caracterização de rizóbios nativos dos Campos Gerais quanto à atividades promotoras do crescimento vegetal e tolerância a estresses abióticos

Abstract

Rhizobia has different mechanisms for promoting plant growth, which are important for plant development and the sustainability of ecosystems. However, abiotic factors (i.g., pH, temperature, and the presence of xenobiotics) can affect symbiotic performance, according to the species/strain analyzed. Previous researches highlighting the occurrence of new species of rhizobia of Campos Gerais region in the Paraná state indicated that the legumes native to this ecosystem are nodulated by phylogenetically

diverse species/strains of rhizobia. Therefore, this study aimed to characterize thirty- six rhizobia strains isolated from root nodules of native specimens of Mimosa spp. and

Desmodium spp. concerning plant growth-promoting activities and responses to abiotic stresses. Strains growth was significantly affected by temperatures of 37°C and 40°C, concentrations of NaCl (1%, 2%, and 3%), and at pH 3.0. While, at pH 4.5 and 6.0 when compared to the control, we did not find significant differences. Such result may be related to the chemical soil conditions of origin of the host plants. Regarding tolerance to heavy metals, although neither of the strains had a positive response to Cu, all the same strains were able to grow at the evaluated concentrations of Zn. Concerning Al, even the highest concentrations tested (i.e., 2mM), 88% of the strains analyzed indicate resistance to these conditions. Neither strain reveal antagonistic activity against phytopathogens tested. Concerning phosphate solubilization activity, about 69.44% of the strains expressed positive results, with solubilization rates ranging from 0.13 to 1.22. Five of the strains produced different quantities of indolic compounds, of which four were isolated to D. barbatum. Our results indicate that abiotic factors significantly and differentially interfered in the growth of rhizobia, and emphasize the importance of physiological characterization in the selection of microorganisms.