Impact of Glomus bagyarajii Inoculation and Phosphorus Amendments on Dry Root-Rot of Chickpea Caused by Macrophomina phaseolina (Tassi) Goid

Dry root rot, caused by Macrophomina phaseolina (Tassi) Goid, is a major constraint in chickpea (Cicer arietinum L.) cultivation, leading to significant yield losses. Conventional chemical management strategies have shown limited efficacy and pose environmental risks, emphasizing the need for sustainable alternatives. This study highlights the potential of arbuscular mycorrhizal fungi (AMF), specifically Glomus bagyarajii, as a biocontrol agent against M. phaseolina. G. bagyarajii was selected based on its proven effectiveness in preliminary studies on chickpea and its strong root-colonizing ability under varying phosphorus (P) conditions. While other AMF species like Glomus macrocarpon and Gigaspora margarita are also commonly studied, G. bagyarajii was chosen for its adaptability to chickpea rhizospheres in semi-arid conditions. We evaluated the effects of G. bagyarajii inoculation and three phosphorus levels (0, 40, and 80 mg P/kg soil) on chickpea growth, mycorrhizal colonization, spore density, and suppression of dry root rot. AMF inoculation significantly enhanced plant growth both in the absence and presence of the pathogen. Dual inoculation of G. bagyarajii with M. phaseolina showed a significant reduction in disease incidence of more than 80 percent, particularly when AMF was applied one week prior to pathogen inoculation. This timing allowed early root colonization and priming of host defense mechanisms. Among the P treatments, 40 mg P/kg soil consistently showed the highest mycorrhizal colonization, spore density, and disease suppression. This intermediate P level may have provided optimal conditions, which are sufficient for plant growth and AMF function without suppressing fungal symbiosis, which can occur under high P availability (80 mg/kg), or limiting plant vigor as seen under P deficiency (0 mg/kg). These findings demonstrate the synergistic interaction between AMF inoculation, application timing, and optimal P fertilization in enhancing plant growth and mitigating pathogen stress. The use of G. bagyarajii under appropriate P regimes presents a promising eco-friendly strategy for integrated disease management in chickpea.