Proliferative response of Rhizobium etli strains to the mixture of common bean exudate and the soil extract

Abstract

The proliferation of two Rhizobium etli strains was examined in a medium containing seed or root exudate obtained from three cultivars of common bean plus a soil extract. Rhizobium etli NOKO-312 died in the medium containing the soil extract and seed exudate of cv. Hokkaikintoki or cv. Kurodanekinugasa. However NOKO-312 proliferated in the medium containing the seed exudate and nitrogen-free plant nutrient (NFPN) solution in place of the soil extract. The bacterial population of NOKO-312 increased on the inoculated seeds of all three cultivars after 24 h in aseptic vermiculite moistened with NFPN solution. These findings suggested that the inhibitory effect on the growth of NOKO-312 was induced when the medium contained both the soil extract and the seed exudate but not root exudate of Hokkaikintoki or Kurodanekinugasa.