NODULATION OF PHASEOLUS-VULGARIS BY RHIZOBIUM-ETLI IS ENHANCED BY THEPRESENCE OF BACILLUS

The ability of Bacillus spp. to alter the nodulation of Phaseolus vulg aris by Rhizobium etli was assessed. The simultaneous presence of both Rhizobium etli TAL 182 and Bacillus megaterium S49 on plant roots dur ing the early stages of plant growth was necessary for enhanced nodula tion of Phaseolus vulgaris by the Rhizobium microsymbiont. Coinoculati on with both bacterial species also facilitated heterologous nodulatio n of Rhizobium TAL 182 on Phaseolus acutifolius. These results are con sistent with earlier reports of increased root hair proliferation and lateral root formation in response to coinoculation. Split-root experi ments revealed that coinoculation partially suppressed host-controlled regulation of nodulation, implicating a plant interaction with the tw o bacterial species. Changes to the nodulation potential of R. etli du e to coinoculation with Bacillus spp. demonstrate the potential for ro ot-associated organisms other than rhizobia to alter the dynamics of t he legume-Rhizobium symbiosis.