Bioprospecting of microbial agents and their metabolites as potential inhibitors of Phytophthora cinnamomi, the causal agent of avocado root rot

Phytophthora Root Rot (PRR) is one of the economically important diseases infecting avocado causing substantial yield losses worldwide. In this study, the root rot pathogen infecting avocado has been characterized and potential bioagents targeting PRR have been identified through molecular approaches. Field surveys revealed varying degrees of disease severity (54 %-17.5 %) and incidence (50 %-10%) in Western Ghats of Tamil Nadu, India. The pathogen was isolated and identified as Phytophthora spp. based on morphology which depicted typical coralloid-type growth patterns. Besides, phylogenetic analysis with the ITS, ras-related protein and COX genes showed closed similarity with P. cinnamomi. The isolates showed significant variation in pathogenicity, with PC(TKI)-10 exhibiting the highest severity (70 %) developing typical symptoms. In vitro efficacy assays through dual-plate and volatiles revealed potential inhibitory effects of Trichoderma harzianum T (MP)-7 (81.11 %) and Bacillus amyloliquefaciens B (TI)-3 (76.67 %) against P. cinnamomi, and Scanning Electron Microscopy (SEM) provided insights into the antagonistic mechanisms, revealing physical interactions and enzymatic lysis of the pathogen by T (MP)-7 and B (TI)-3. Furthermore, Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified bioactive compounds in the crude extracts of these bioagents, elucidating their metabolic pathways and potential modes of action against P. cinnamomi. Our findings highlights the importance of P. cinnamomi in avocado and the mechanism of fungal and bacterial bioagents in the sustainable management of the disease.