Carboxymethyl chitosan promotes biofilm-formation of Cryptococcus laurentii to improve biocontrol efficacy against Penicillium expansum in grapefruit

The synergistic effectiveness of the yeast Cryptococcus laurentii cultured with carboxymethyl chitosan (CMCS) at different concentrations was studied in controlling Penicillium expansum in postharvest grapefruit and exploring the biofilm formation mechanism. The current research results indicate that 0.5% (w/v) CMCS - treated C. laurentii for 72 h could suppress Penicillium expansum conidia germination and hyphal growth in vitro on grapefruit, and its biocontrol efficacy had been significantly enhanced. Moreover, population number of C. laurentii induced by low CMCS level in vitro was obviously increased by changing the budding capacity of yeast. In in vitro experiments, CMCS -C. laurentii adhered to the orifice plate, having a strong biofilm-forming ability, and accompanied by the production of extracellular secretions. Furthermore, the monosaccharide composition of extracellular polysaccharides of yeast by inducing treatment was determined. Among these, compared with C. laurentii , the contents, such as Ara, Gal, Xyl, Man, and Glc-UA, all were increased. Adhesive substances wrapped on the surface of yeast and accompanied by a thin reticular structure were further observed by scanning electron microscopy. Meanwhile, we identified that C. laurentii tightly adhered to the hyphae indicating that the induction treatment effectively inhibits the pathogen development. In comparison to the control fruit, 0.5% (w/v) CMCS-cultured yeast resulted in noticeably synergistic effects that greatly decreased the grapefruit blue mould decay rate and lesion diameter. A new idea was presented in this study to enhance the biocontrol properties of antagonistic yeast.