GROWTH AND NODULATION COMPETITIVENESS OF SINORHIZOBIUM-MELILOTI L1 (RECA(-)) IS LESS-THAN THAT OF ITS ISOGENIC STRAIN L33 (RECA(-MELILOTI WILD-TYPE ISOLATES()) BUT COMPARABLE TO THAT OF 2 SINORHIZOBIUM)

Gnotobiotic systems were used to assess the competitive abilities of b ioluminescent Sinorhizobium meliloti strains L1 (RecA(-)) and L33 (Rec A(+)) for growth and host plant nodulation in the presence of a recons tructed S. meliloti population. Three wild-type strains belonging to i nfective subgroups of a natural S. meliloti population were chosen as competitors in microcosm studies. Whereas the RecA(+) strain L33 domin ated the reconstructed population with respect to growth and alfalfa n odulation, the competitiveness of the RecA(-) strain L1 was reduced co mpared to that of one of the field strains, but comparable to that of the other field isolates. This result indicates that strain L1, despit e its recA mutation, has the potential to compete successfully with a resident S. meliloti population after environmental release.