Exploiting <scp> <i>Paraphaeosphaeria minitans</i> </scp> and Its Antifungal Metabolites as Bio‐Fungicides for Eco‐Friendly Management of Head Rot Disease in Cabbage

Cabbage head rot, caused by Sclerotinia sclerotiorum, threatens crop yield and quality. Among the 21 mycoparasitic fungi isolated from sclerotia, dormant structure and primary sources of inoculum for the pathogen, the strongest antagonism (78.51% mycelial growth inhibition) was observed in Paraphaeosphaeria minitans strain TNAU-CM 1. Scanning electron microscopy (SEM) revealed its destructive colonisation, including pycnidia and pycnidiospore formation, with visible shrinkage and deformation of sclerotia. Gas chromatography-mass spectrometry (GC-MS) analysis identified 24 bioactive metabolites at the point of interactions between P. minitans TNAU-CM 1 and S. sclerotiorum TNAU-SS-5 strains in dual-culture assays. Further, crude metabolites from P. minitans TNAU-CM 1 cultures inhibited the pathogen's mycelial growth by 54.4% at 100 ppm. In the molecular docking of 14 key compounds, linoleic acid and butyl octyl phthalate, well-known antifungal compounds, displayed the highest binding affinity of -7.6 and -6.2 kcal/mol, respectively, against Saccharomyces cerevisiae cupin protein (1ZNP) YML079w, a homologue of SsYCP1, a YML079-like cupin protein (YCP) and a virulence molecule from S. sclerotiorum. Field trials demonstrated that foliar application of P. minitans TNAU-CM 1 stock solution (8-10 × 10⁸ spores per mL) at 5 mL/L dilutions significantly reduced disease incidence and the crops produced a yield of 41.37 tons/ha, comparable to chemical fungicide treatment (43.51 tons/ha). Thus, molecular interaction studies and field evaluations suggest that P. minitans TNAU-CM 1 is a promising eco-friendly alternative to synthetic fungicides for the management of cabbage head rot. Furthermore, our findings indicate that linoleic acid and butyl octyl phthalate are the key antifungal metabolites of P. minitans, active against S. sclerotiorum and will serve as potential candidates for developing bio-fungicide formulations to control head rot in cabbage.