Biocontrol ability and possible mechanism of Metschnikowia pulcherrima against major diseases of postharvest citrus fruit and its biopreservative application

The capability of Metschnikowia pulcherrima to control postharvest citrus diseases was analyzed, with its action mechanisms and preservation performance during storage further explored. In vitro and in vivo tests demonstrated M. pulcherrima significantly inhibited the growth of Penicillium digitatum (P.d), Penicillium italicum (P.i), and Geotrichum citri-aurantii (G.c), and markedly controlled the incidence and progression of these three postharvest diseases. The non-cellular components of M. pulcherrima did not significantly inhibit three pathogens' growth, while its volatile compounds (VOCs) displayed notable inhibitory effects. Moreover, M. pulcherrima exhibited no parasitic effects on the mycelia of three pathogens. Nutritional competition experiment revealed that M. pulcherrima outcompeted the pathogens, utilizing fructose and glucose more rapidly and efficiently in nutrient-poor fruit wounds. Additionally, M. pulcherrima demonstrated a rapid proliferation and colonization ability on citrus fruit wounds and exhibited biofilm formation, thereby effectively preventing pathogen from contacting the fruit. Iron competition experiments indicated that exogenous FeCl₃ significantly reduced M. pulcherrima's antifungal activity against P.d, P.i, and G.c, and its diseases control efficacy. Induced resistance tests demonstrated that M. pulcherrima significantly enhanced citrus fruit resistance to three diseases, with a particularly strong effect against sour rot. Storage tests over 180 d revealed that M. pulcherrima treatment significantly decreased the natural decay rate and maintained the quality indicators of citrus fruits. Overall, M. pulcherrima presented considerable potential as a biocontrol agent for effectively managing postharvest diseases in citrus fruits.