Evaluación de la capacidad de fijación del nitrógeno atmosférico de las bacterias asociadas con la rizosfera de plantas de Solanum tuberosum L. Var. Superchola en la provincia de Tungurahua

Abstract

The present study was developed with the purpose of isolating, quantifying, characterizing, evaluating and conserving free-living bacteria associated with the potato rhizosphere with atmospheric nitrogen fixation capacity, from soil samples from four localities in the province of Tungurahua. First, soil samples were collected from the potato crop and placed in plastic containers of 6 L capacity, where tubers of the Superchola variety were planted. After 60 days, samples of rhizospheric soil (area near the roots) were extracted. For isolation, the pour plate method was used in Jensen culture medium free of nitrogen sources. To quantify viable bacteria per gram of soil from each locality, serial solutions were prepared where 100 µl were deposited in solid medium, incubated for 72 hours at 30 ºC in inverted position and the plate count was performed. The locality of Santa Rita in the canton of Pillaro had the highest number of CFU/g of soil. A total of 72 isolates were obtained from the potato rhizosphere, of which only 38 isolates produced a positive reaction with the color change of the medium modified with bromothymol blue from green to blue, these were subjected to morphological and cultural characterization. In relation to morphology, 84% were predominantly Gram (-) bacteria, bacilli (95%) and their grouping was mostly in the form of diplobacilli (37%). In the cultural characterization, the following shapes predominated: circular (42%), entire margin (84%), smooth texture (87%), flat surface (42%), smooth consistency (82%) and 95% showed brightness. The bacterial isolate with the greatest capacity to fix atmospheric nitrogen was (T1-FCAGP-BFN1) from the El Placer sector of the Quero canton, which had no statistically significant difference with respect to isolates T3-FCAGP-BFN14, T3-FCAGP-BFN16 and T4- FCAGP-BFN24. The purified isolates were deposited in eppendorf tubes with 15% glycerol and BHI liquid medium + 20% glycerol and stored at -20 ºC. The bacterial isolates with the highest nitrogen-fixing capacity obtained could be used to determine their plant growth-promoting activity in greenhouses prior to their possible use as biofertilizers under field conditions.