Rhizobium isolates nodulating common bean: A pathway to control Fusarium sp, the causative agent of damping-off of seedlings

Obtaining a high-performing inoculant requires combining diversified traits that can strongly contribute to promoting plant growth and protection. This work aims to contribute to developing biological control of Fusarium sp., the causative agent of damping-off using rhizobia. Eight rhizobial isolates from the Laboratory of Plant Biology were used. A search for some enzymes (cellulase, proteases, chitinases, and phosphatases) produced by rhizobia and involved in biological control was carried out. The rhizobia isolates were then tested for their ability to biocontrol Fusarium sp. in direct and indirect confrontation. Finally, the effect of inoculation with the isolates on the growth of bean plants and the severity of Fusarium sp. was assessed. The results show that all the bacterial isolates can synthesize lytic enzymes in varying proportions, while 50% could produce phosphatases. The direct antagonism test against Fusarium sp. showed that the isolates exert inhibitions ranging from 20.55% to 65.15% and 30% to 30.8% in indirect confrontation. The results of the effect of inoculation of infected plants on plant growth and pathogen severity indicate that the tested Rhizobium isolates promote the growth of infected plants by causing a decrease in disease as well as significant improvement in the height of the stems compared to non-inoculated plants. These results, therefore, indicate that the rhizobia isolates used considerably reduce the growth of Fusarium sp. using enzymes and antagonistic substances, leading to improved growth of bean plants.