The in vitro inhibition of Phytophthora clandestina by some rhizobia and the possible role of Rhizobium trifolii in biological control of Phytophthora root rot of subterranean clover

The interaction between 29 isolates of Rhizobium and the in vitro growth of 3 strains of Phytophthora clandestina was investigated to determine the po tential of these bacteria as biological control agents against root rot of subterranean clover (Trifolium subterraneum L.). The biological control act ivity of Rhizobium on the severity of root disease in seedlings was also in vestigated under glasshouse conditions. Thirteen of the 29 Rhizobium isolat es caused significant reductions in the hyphal growth of the 3 P. clandesti na isolates examined. Inoculation of seedlings with Rhizobium trifolii redu ced the severity of root disease by 14-58% with corresponding increases in dry matter production of 20-73%. These results indicate that Rhizobium spec ies have potential as biological control agents against the root rot of T. subterraneum seedlings caused by P. clandestina.