Bioagent‐Mediated Suppression of Fusarium Wilt Disease Complex in Guava Through Enhanced Plant Defence Responses

ABSTRACT

The guava wilt complex, caused by the interaction between root‐knot nematodes and soil‐borne fungi, is a major constraint on guava production. The present study investigated the roles of Meloidogyne incognita and Fusarium oxysporum f. sp. psidii in disease development and evaluated bioagent‐based management strategies under screenhouse and field conditions. Interaction studies showed that nematode inoculation one week prior to fungal infection resulted in maximum disease severity, with higher wilt incidence (72.5%), gall formation (31.7 galls plant ⁻¹ ) and reduced plant height (18.0 cm) compared to other treatments. Among management strategies, neem cake enriched with Bacillus amyloliquefaciens and Trichoderma viride significantly improved plant growth and reduced nematode population (up to 64.0%). The combined application of B. amyloliquefaciens , T. viride and Glomus fasciculatum resulted in greater suppression of nematode population (64.8%) and enhanced plant growth, along with increased accumulation of phenolics (7.10 mg g ⁻¹ ), chlorophyll (41.7 mg g ⁻¹ ) and defence enzymes (PAL: 4.73 U mg ⁻¹ protein; peroxidase: 7.57 ΔOD min ⁻¹  g ⁻¹ FW). Multivariate analysis revealed strong negative associations between nematode parameters and yield. Under field conditions, integrated application of bioagents, marigold and minimal chemical input reduced nematode population (70.6%) and increased yield (19.9%) over control, with the highest economic return. These findings demonstrate that targeting nematode–fungus interactions through bioagent‐mediated approaches offers a viable and sustainable strategy for managing guava wilt complex under field conditions.