A critical review of biological control strategies for powdery mildew of bhendi (Abelmoschus esculentus L.)

Powdery mildew caused by Golovinomyces cichoracearum is a major constraint in bhendi (Abelmoschus esculentus L.) production, leading to significant yield and quality losses under favourable environmental conditions. This review aims to synthesise current knowledge on the biology, epidemiology and molecular interactions of the bhendi-powdery mildew pathosystem, with emphasis on sustainable management through biological control agents. The pathogen establishes a biotrophic relationship via haustorial development and effector-mediated suppression of host immunity, while host defence involves pattern-triggered immunity and effector-triggered immunity, including reactive oxygen species production and callose deposition. Biological control agents such as Ampelomyces quisqualis, Trichoderma spp. and Bacillus spp. exhibit diverse mechanisms including hyperparasitism, mycoparasitism, antibiosis and induction of systemic resistance. These agents enhance plant defence through increased activity of key enzymes such as peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase, contributing to reduced disease severity. Advances in formulation technologies, including talc-based carriers, alginate encapsulation and oil-assisted delivery systems, have improved the efficacy and field stability of these agents. Integrated approaches combining compatible biological control agents and low-risk chemicals provide enhanced disease suppression compared with single-agent applications. However, variability in field performance, environmental constraints and limited molecular understanding of pathogen diversity remain key challenges. Future strategies integrating omics-based approaches, genome editing and climate-informed disease prediction are essential for improving the consistency and effectiveness of biological control. Overall, biological control integrated within sustainable management frameworks offers a viable alternative to chemical fungicides for managing powdery mildew in bhendi.