Rhizobium leguminosarum symbiovar viciae strains are natural wheat endophytes and can stimulate root development and colonization by arbuscular mycorrhizal fungi

Although rhizobia establishing a nitrogen-fixing symbiosis with legumes are also known to promote growth in non-legumes, studies on rhizobia association with wheat roots are scarce. We searched for Rhizobium leguminosarum symbiovar viciae (Rlv) strains naturally competent for wheat roots colonization. We isolated 20 strains and tested the ability of a subset for wheat roots colonization when co-inoculated with other Rlv. We also measured the effect of these strains on wheat root architecture and Arbuscular Mycorrhizal Fungal (AMF) colonization. We found a low diversity of Rlv in wheat roots compared to that observed in the Rlv species complex. Only a few strains, including those isolated from wheat roots, and one strain isolated from pea nodules, were efficient to colonize wheat roots in co-inoculation conditions. These strains had a high ability for endophytic colonization of wheat root and were able to stimulate root development and AMF colonization in single strain inoculation conditions. These results suggest that wheat is an alternative host for some Rlv; nevertheless, there is a strong competition between Rlv strains for wheat root colonization. Furthermore, our study suggests that the level of endophytic colonization is critical for Rlv ability to promote wheat growth.