Rizobactérias da bacaba (Oenocarpus bacaba Mart.) – Tolerância ao alumínio e potencial como promotoras do crescimento de plantas

Abstract

Acidic soils with high concentrations of trivalent aluminum (Al3+) are associated to low crop productivity due to the inhibition of root growth. Plant growth promoting bacteria (PGPB) are important tools in the agriculture, being able to improve plant nutrition and tolerance to biotic and abiotic stresses. The objective of this research was to prospect, from the rhizosphere of bacaba plants (Oenocarpus bacaba Mart.), PGPB capable of reducing the Al3+ stress in soybean and maize. A total of 207 bacterial isolates were obtained from the root and the rhizospheric soil (SR) of bacaba, among which 31 were able to grow after being cultivated in Luria-Bertani (LB) medium with 14.8 mM AlCl3 at pH 4. Those bacteria were identified by 16S rDNA gene sequencing and evaluated in vitro for the production of auxins, ACC-deaminase and siderophores, nitrogen fixation and phosphate solubilization. Four strains were selected among the most promising isolates to be used in greenhouse experiments with soybean and maize, in order to verify their plant growth-promoting efficiency in a situation of Al3+ stress. The isolates of Klebsiella sp. SR-1, SR-15, SR-76, and Pantoea sp. SR-98 presented positive results in all in vitro assays. In maize, isolates SR-1, SR-15 and SR-76 improved root biomass. In soybean, all tested isolates produced higher plants compared to the control. When associated to maize, all treatments reduced the percentage of Al saturation of the rhizospheric soil, especially isolate Klebsiella sp. SR-15, which reduced this index by 80%. In soybean, all the treatments increased the Al saturation of the soil in comparison to the non-inoculated control. Therefore, the results obtained indicate that the interaction of PGPB with different plant species might produce opposite results. Also, this study raises the possibility of mitigating Al-stress in plants growing in acidic soils by using PGPB, while promoting greater productivity and also reducing the costs with chemical inputs.