Effects and possible modes of action of Kloeckera apiculata for controlling Penicillium expansum in apples

• K. apiculata reduced the colony diameter and mycelial weight of P. expansum . • Yeast parasitized on the mycelial, and culture showed maximum inhibition. • Yeast reduced the decay incidence and lesion diameter of apples. • Yeast roles involve nutrient and space competition, parasitism, induced resistance. Kloeckera apiculata is a yeast strain with excellent biocontrol capacity. The strain can effectively control a variety of postharvest diseases in fruit. However, the effect of the yeast control on blue mold caused by Penicillium expansum in apples and its related mechanisms have rarely been reported. In this study, the colony diameter and mycelial weight of P. expansum were reduced with varied doses of K. apiculata treatment. Compared with controls, the colony diameter and weight of P. expansum mycelial treated with 1 × 10 8 cell/mL of yeast were 63 % and 70 % lower, respectively. The original yeast culture treatment exhibited the highest inhibition, followed by the culture filtrate, while inactivated culture filtrate displayed no significant inhibitory effect. Results from scanning electron microscopy demonstrated that yeast parasitizes mycelial surfaces, thereby reducing survival and damaging mycelial integrity. Moreover, yeast rapidly colonized apple wounds, reducing decay and lesion diameter. The yeast treatment upregulated the activity of superoxide dismutase, catalase, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase, and increased total phenols, flavonoids, and lignin content of the fruit. K. apiculata may directly inhibit the growth of P. expansum through competition for nutrients and space, and via parasitism. The yeast could also induce resistance against P. expansum by eliciting antioxidant enzymes and phenylpropanoid metabolism.