Rhizobium spp. Isolates as Biocontrol Agents of Bean Damping-off, Caused by Rhizoctonia solani

The antagonistic effects of Rhizobium spp. isolates against Rhizoctonia solani (AG-4), the causal agent of bean damping-off were compared with each other in either of the in vitro and in vivo conditions. Also their potential to produce such secondary antifungal metabolites as HCN, siderophore and protease were evaluated. The results indicated that, isolate RH3 reduced mycelial growth of R. solani more than the others did in vitro conditions. Isolates RH4, (RH6, RH3) and RH6 produced the highest siderophore, protease and HCN, respectively. Under greenhouse conditions, strilized soil was used to evaluate the effect of seed coatings with bacterial isolates on disease incidence, percentage of disease control and as well on growth factors. Isolates RH5 and RH4 indicated the highest level of plant dry weight in the presence of pathogen. Although none of the bacterial isolates could suppress the disease completely under greenhouse conditions, RH3 isolate could control the disease to an extent more than 80%. The obtained results indicated that the biocontrol potential of Rhizobium isolates not only led to an alleviation of the disease but also promoted plant growth. Then such bacterial isolates can be successfully applied in sustainable agricultural production systems.