Preharvest glycerol treatment enhances postharvest storability of orange fruit by affecting cuticle metabolism

Although cuticle is known to play an important role in the biotic and abiotic stress resistance of citrus fruit, there has been rare research on preharvest exogenous treatments to regulate cuticle metabolites and improve the postharvest storability of citrus fruit. In this study, the effect of spraying 10% glycerol 90 days before harvest on cutin, wax, fruit storability, and primary metabolites of citrus fruit was analyzed. The results demonstrated that exogenous glycerol could promote the biosynthesis of cutin at the early stage and delay the degradation of wax at the later stage of treatment, which could be attributed to the induction of genes associated with cuticle metabolism. Among them, the expression of CsLACS1, CsLACS2, CsCYP86A8, and CsMYB106 showed the highest correlation with cutin metabolism. Exogenous glycerol could further reduce postharvest water loss, decay, respiration rate, and accumulation off-flavor compounds such as acetaldehyde and ethanol, thereby improving fruit storability. Moreover, exogenous glycerol showed no effect on fruit quality before harvest, and the low levels of stress-response metabolites (such as γ-aminobutyric acid) suggested that glycerol-treated fruit were in a less stressful state compared to control fruit. In conclusion, preharvest glycerol treatment may be a safe and effective method to improve citrus fruit storability by regulating cuticle metabolism.