Symbiotic performance of some modified Rhizobium etli strains in assays with Phaseolus vulgaris beans that have a high capacity to fix N2

Rhizobium etli and R. tropici form nitrogen-fixing nodules on Phaseolus vulgaris (common bean). In the hope that R. etli strains with additional citrate synthase genes have better carbon economies, merodiploid strains were constructed. Previously, one such construct was shown to have an increased nodulation capacity in the standard bean cultivar Negro Xamapa. In the present work, derivatives from different R. etli strains carrying the R. tropici plasmid-borne or chromosomal citrate synthase gene were constructed and tested for nodulation in bean cultivars selected for their high capacity to fix nitrogen. Nodule numbers were dependent on the strain and the cultivar used. Differences in nodule number were not reflected in plant biomass.