Resumo

The maize is considered one of the most important cereals in the world. To obtain high yields in the current patterns of agriculture are necessary processes that make responsible use of natural resources. In this context, plant growth promoting rhizobacteria can contribute to the plant development through multiple mechanisms of action. The aim of the present study was to identify and select isolated rhizobacteria from Amazon guarana that are able to fix N₂, solubilize calcium phosphate, produce IAA and siderophores (substances that are often related with plant growth promotion) and to evaluate the potential of corn growth promoted by these isolated. Physiological changes, like nutrients accumulation, were also monitored. 107 rhizobacteria were isolated from the guarana plants and then identified by partial sequencing of 16S rDNA. For the evaluation of N₂ fixation, a qualitative essay was made. To verify phosphate solubilization, production of siderophore and IAA, quantitative and semi-quantitative essays were made. From this initial screening, five isolated were selected to be tested in a greenhouse experiment: RZ1MS6, RZ1MS11, RZ2MS9, RZ2MS16 and RZ4MS18, all belong to the genus Burkholderia, except the isolate RZ4MS18 that belongs to the genus Delftia. Bacterial cells were applied in corn seeds. The plants were sampled 30 and 60 days after inoculation (DAI). Height and dry mass of shoot and root parts were quantified. In the evaluated bacterial community was observed the predominance of the genera: Burkholderia (32%), Bacillus (30%), Ralstonia (12%) and others. Among 107 bacterial isolated, 33% presented potential to fix N₂, 41% solubilized calcium phosphate and 22% produced siderophore, most of them belongs to Burkholderia genus that also showed the highest production of IAA. The Isolated RZ2MS9 and RZ2MS16 increased approximately 40% and 35% respectively the plant height with 30 and 60 days, comparing with the control. The consortium showed no significant difference in height comparing with the control. Interestingly, the isolate RZ2MS9 increased more than 230% and 240% the shoot and root dry weight, respectively, at 60 DAI comparing with the control. The isolate RZ2MS16 also showed good results, increasing more than 110% and 140% the shoot and root dry weight, respectively, at 60 DAI comparing with the control. The treatments tested also showed changes in the concentration of nutrients like Ca, Cu, S, Fe, P, K and Zn. The biotechnological potential of bacteria from tropical climates should be further explored aiming to increase sustainable production. In a next step, will be evaluated their effects on another crops of agricultural interest.