Compétition entre souches de Rhizobiaceae: mise en évidence de différents modes d'adhésion sur les racines de soja

Abstract

Adhesion of 11 Rhizobiaceae strains on soybean roots was investigated. Whether these strains were able or not to nodulate soybean, they were found to adhere to these roots. Bacterial concentration above 1 × 1010 cells∙mL−1 was necessary to saturate root surfaces. Homologues and heterologous strains were used in mixed inoculation with Bradyrhizobium japonicum G49 StrR, used as reference strain in low number. Competition for adhesion was obtained at saturating concentrations of competitive strains. Only partial inhibition (< 55%) of the G49 StrR strain adhesion in the presence of heterologous strains was obtained, suggesting the occurrence of two modes of G49 StrR strain adhesion on the host roots: (i) a nonspecific adhesion of the B. japonicum and (ii) a specific adhesion of the B. japonicum or of strain G49 StrR. With homologous strains, inhibition of G49 StrR strain adhesion indicated a different competitive behavior between the four strains used belonging to the two DNA homology groups. Thus, the existence of species-specific recognition for all strains of B. japonicum, on soybean roots, remains to be confirmed.Key words: Rhizobiaceae, soybean, competition, adhesion, root.