Biological control of blue mold rot in apple by Kluyveromyces marxianus XZ1 and the possible mechanisms of action

The yeast Kluyveromyces marxianus was permitted for direct addition to food and shown antagonistic ability against some pathogens. However, the effect and detailed mechanism of K. marxianus on control blue mold disease and patulin accumulation in apple remain unknown. In our study, K. marxianus XZ1 reduced the disease incidence and patulin content in apple caused by Penicillium expansum at 3 d after incubation compared with the control, which is decreased by 51% and 52%, respectively. Studies on the potential mechanisms of action revealed that (1) K. marxianus XZ1 adhered well to the apple wound to gain a competitive advantage; (2) antibacterial substances produced by K. marxianus XZ1 under the stimulation of P. expansum to inhibit the growth of this fungus; (3) activity of catalase, peroxidase, polyphenoloxidase, chitinase, and phenylalanine ammonialyase was activated to participate in the defense of fruit against P. expansum; (4) the expression levels of some genes involved in plant hormone signal transduction, including salicylic acid, jasmonate acid and ethylene signaling pathway, were upregulated to strengthen the fruit's defense against mold. Taken together, our results indicated that K. marxianus XZ1 may serve as a potential biological agent against postharvest decay and patulin contamination caused by P. expansum in apple fruit, mainly attributed to its ability of competition for space and nutrients, secretion of antifungal components, parasitism and activation of plant hormone signal transduction.