The use of gus-reporter gene technique in the assessment of the competitive ability of Rhizobium etli nodulating Phaseolus vulgaris L. from the acidic soils of La Trinidad, Benguet, Philippines

Abstract

Rhizobia bacteria are agriculturally important microorganisms that form nodules on the roots of legumes. Acid-tolerant rhizobia could act as biological fertilizers in acid soils and the use of rhizobial strains in agriculture is more economical and a more environment-friendly technology. Using the gus maker gene, two new rhizobial isolates from La Trinidad, Benguet were tested for their nodulation competitiveness, i.e., the acid-tolerant, Rhizobium etli, RG-136 and the acid-sensitive Rhizobium etli RG-57, in comparison with a well studied acid-tolerant reference strain Rhizobium tropici UMR-1899. Two gus-marked derivatives were obtained and their competitive abilities were compared with their wild type parent strains and the reference strain using greenhouse experiments. Statistical analyses revealed that the wild type parent strains gave significantly higher nodule occupancies compared with the two gus-marked derivatives, indicating that the gus marker gene may not be a suitable genetic marker for the acid tolerant strains used in this study.