Evaluating the efficacy of rhizobium isolates as biological control agents against bacterial canker in tomato plant

This study investigates the potential of rhizobium isolates from Bean plant nodules, as biological control agents, against Clavibacter michiganensis subsp. michiganensis (Cmm) in Tomato plants grown in untreated soil in the Chtouka Ait Baha province (Morocco). A total of 14 distinct rhizobium isolates were isolated and characterized through morphological, biochemical, and enzymatic analyses. The antagonistic capacity of the rhizobium isolates against Cmm was evaluated using an in vitro co-inoculation technique on nutrient agar. greenhouse trials, twenty-day-old tomato seedlings were irrigated with the bacterial suspension before being inoculated with Cmm. Among these isolates, five demonstrated significant antagonistic activity in vitro against Cmm, with isolate RF8 exhibiting the highest inhibition rates of 19.9% against Cmm. in greenhouse experiments the result showed that these five isolates   effectively reduced disease incidence and severity in tomato plants. Notably,isolate RF3 demonstrated a significant reduction, exhibiting a lower incidence rate of 26.66%, in comparison to the positive control group with a rate of 90%. Furthermore, RF3, RF8, and RF11 demonstrated significant decreases in the severity of the Cmm disease with 1.6 and 1.7 respectively, compared to the control. The presence of various hydrolytic enzymes, including cellulase, pectinase, and chitinase, among the rhizobium isolates indicates a multifaceted approach to biocontrol, which may enhance disease resistance mechanisms in plants. This study not only highlights the promising role of rhizobium isolates in managing plant diseases but also emphasizes their potential for integrating sustainable agricultural practices. Future research should focus on exploring the underlying mechanisms of action, optimizing field application methods, and assessing the long-term effects of these isolates in crop protection. The findings pave the way for utilizing rhizobium as eco-friendly biocontrol agents, contributing to healthier crops and reducing reliance on chemical pesticides. Keywords: Antagonistic activity, biological control, Clavibacter michiganensis subsp. Michiganensis, Rhizobium, Tomato.