Carboxymethyl cellulose-induced Cryptococcus laurentii improves disease resistance and regulates phenylpropane and reactive oxygen metabolism in grapefruit

Green mould disease poses a significant threat to the citrus industry. Cryptococcus laurentii can stimulate the fruit defence system, whereas the use of antagonistic yeast alone demonstrates limited efficacy. This study investigated the molecular mechanisms of C. laurentii cultured with carboxymethyl cellulose (CMCC. laurentii), and evaluated the effects of CMCC. laurentii on phenylpropane and reactive oxygen metabolism in grapefruit fruit. Transcriptome analysis revealed that the upregulation of gene expression associated with yeast growth and antagonistic ability occurred in CMCC. laurentii after 72 h cultivation. Meanwhile, CMCC. laurentii reduced lesion diameter and disease incidence in fruit. This treatment promoted phenylpropane metabolism by activating PAL, C4H, 4CL, POD, and PPO and increasing the secondary metabolites. CMCC. laurentii also activated the AsA-GSH cycle, enhanced the activities of SOD and CAT, and reduced the accumulation of H₂O₂ and O₂^•-. The results suggested that CMCC. laurentii maintained high postharvest fruit quality in grapefruit fruit by elevating the phenylpropane and reactive oxygen metabolism.