Biological control of green mould on mandarin fruit through the combined use of antagonistic yeasts

Penicillium digitatum is the primary cause of green mould in mandarins during the postharvest period, mainly controlled through synthetic fungicides. This study evaluated the biocontrol of green mould on mandarin fruit with three antagonistic yeasts (Hanseniaspora uvarum, Meyerozyma guilliermondii, and Metschnikowia aff. pulcherrima P01A016), alone or in combination, by elucidating their possible mechanisms of action. All yeast cultures alone (73.85 % − 80.64 %) and their combinations (78.40 % − 83.18 %) reduced the mycelial growth of green mold in vitro. M. aff. pulcherrima reduced the disease incidence and lesion diameters by 75.5 % and 91.3 %, respectively, demonstrating the highest biocontrolling activity alone. Meyerozyma guilliermondii showed the highest biofilm formation (OD 0.93 ± 0.01) and antifungal activity (71.13 %) through volatile organic compounds (VOCs), while H. uvarum displayed cell-wall degrading β-1,3 glucanase activity together with mycocinogenic and VOCs activity. All tested yeasts showed chitinase, protease, and leucine arylamidase activity. Among dual combinations, M. guilliermondii and M. aff. pulcherrima (M-1) were the most compatible, while M. aff. pulcherrima and H. uvarum (M-3) had the least compatibility. The combined application of these three yeasts resulted in synergistic co-operation, demonstrating the highest biocontrolling efficacy in vitro and in vivo. Integrating multiple mechanisms of action in yeasts could create a hurdle approach for inhibiting green mould in citrus as a green alternative to synthetic fungicides. Thus, our study demonstrated that combining biocontrol yeasts can result in beneficial consortia for the eco-friendly and sustainable management of P.digitatum-caused postharvest diseases of mandarins in both the wounded and intact mandarin fruits.