COMPETITION AMONG RHIZOBIACEAE STRAINS - EVALUATION OF DIFFERENT ADHESION MODES ON SOYBEAN ROOTS

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 x 10( 10) cells . mL-1 was necessary to saturate root surfaces. Homologues a nd heterologous strains were used in mixed inoculation with Bradyrhizo bium japonicum G49 Str(R), used as reference strain in low number. Com petition for adhesion was obtained at saturating concentrations of com petitive strains. Only partial inhibition (< 55%) of the G49 Str(R) st rain adhesion in the presence of heterologous strains was obtained, su ggesting the occurrence of two modes of G49 Str(R) 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 Str(R). Wit h homologous strains, inhibition of G49 Str(R) strain adhesion indicat ed a different competitive behavior between the four strains used belo nging to the two DNA homology groups. Thus, the existence of species-s pecific recognition for all strains of B. japonicum, on soybean roots, remains to be confirmed.