Efficiency of Nitrogen Fixation by Rhizobium Strains Associated With White Clover in the Ecuadorian Highlands Biological Nitrogen Fixation by White Clover in Ecuador

The objective of this research was to evaluate the nitrogen-fixing capacity of 30 strains of Rhizobium isolated from white clover nodules, collected in the provinces of Pichincha and Cotopaxi under greenhouse conditions. After isolation of the bacteria and authentication of the isolates, a greenhouse experiment was conducted, in a Completely Randomized Design (CRD), with three replications and two controls: with and without nitrogen fertilization, using sterilized pomine as substrate. Superficially disinfected white clover seeds were germinated in vitro, transplanted into pots, and inoculated with the bacteria. Fertilization and irrigation were provided with Jensen's solution. Plants were harvested after 90 days of growth, and data were taken on the number and diameter of the nodules, dry weight and nitrogen content of the shoot. Highly significant differences were detected between Rhizobium strains in the five variables evaluated, and with the controls, in dry matter and nitrogen content. A high positive correlation was evidenced between the five variables evaluated. Principal component analysis explained 89.9% of the total variation. It is concluded that seven strains from Pichincha (PI44, PI42, PI41, PI40, PI36, PI34 and PI20) and six from Cotopaxi (CO63, CO60, CO55, CO54, CO49 and CO46), are promising and merit additional studies.