Combined Application of Chitosan-Induced Wickerhamomyces anomalus and Bacillus subtilis to Control Blue Mold Disease of Table Grapes

Abstract

Blue mold decay caused by Penicillium expansum is a major disease of table grapes, causing substantial economic losses. With increasing environmental concern and consumer interest in chemical-free products, eco-friendly biocontrol strategies are necessary. The strains of Wickerhamomyces anomalus incubated with chitosan (WaC) and Bacillus subtilis (Bs) are already reported for their promising efficiency to control blue mold disease caused by P. expansum. However, their individual application is less effective compared to chemical fungicides. The current study determined combined application of these two prominent antagonistic microbes against blue mold decay of grapes. Initially we carried out a compatibility study which confirmed that there was no mutual inhibition among the strains, enabling synergistic formulations. An in vitro study showed that the combined application of WaC and Bs better reduces P. expansum colony diameters at a 4:1 ratio. This ratio also maximally suppressed the pathogen spore germination (62% reduction) and germ tube elongation (67% reduction). The in vivo studies also showed that WaC + Bs (at 4:1) significantly minimized lesion diameters and decay rates of grapes during the 13-day storage, outperforming individual applications. The physicochemical quality parameters of table grapes were also better preserved. The treatments modulated antioxidant and defense enzymatic activities such as PPO, POD, PAL, APX, SOD, and CHI. The elevated phenolic and flavonoid contents, with strong positive correlations among the enzymes, underscored the induced resistance of the host. These findings highlight the synergistic potential of chitosan-enhanced Wa with Bs for effective, sustainable postharvest biocontrol, extending grape shelf life and reducing chemical reliance.