The application of Cryptococcus laurentii induced by carboxymethyl chitosan remodeled the microbiome of fruit peel and reduced postharvest green mould in grapefruit

The grapefruit industry faces a major challenge from postharvest diseases caused by Penicillium spp. Biological control is becoming increasingly acknowledged as an effective alternative to chemical fungicides for managing these diseases. This study examined the biocontrol efficacy of Cryptococcus laurentii , induced by carboxymethyl chitosan (CMCS- C. laurentii ), against postharvest diseases, and assessed the microbiota present on grapefruit peel using amplicon sequencing techniques. The results demonstrated that CMCS- C. laurentii significantly reduced decay incidence and induced more pronounced changes in fungal diversity than bacterial diversity within the microbiota. Notably, the treatment group exhibited a significant enrichment of the genus Papiliotrema ( Cryptococcus ), while the genera Zasmidium , Penicillium , and Cladosporium were reduced relative to the control group. Furthermore, CMCS- C. laurentii preserved fruit quality and minimized color change in grapefruits. The results suggest that CMCS- C. laurentii has the potential to mitigate plant pathogens, reduce the incidence of fruit diseases, and maintain high-quality postharvest grapefruits by inducing modifications in the bacterial and fungal communities. • CMCS- C. laurentii reduced disease in vitro and grapefruit fruit. • CMCS- C. laurentii retarded the change of color, and maintained the quality of grapefruit fruit. • CMCS- C. laurentii regulates microbial community composition. • Cryptococcus could colonize grapefruit peel and inhibit pathogen growth. • Positive correlations were observed between Cryptococcus abundance and fruit quality.