Preharvest CPPU Application Improves Litchi Fruit Storability via Modification of Hormone Profiles and Maintenance of...

Litchi (Litchi chinensis Sonn.), an important fruit in south China, rapidly loses commercial value within 3-4 days at ambient temperatures due to poor storability. Previous studies have shown that 5 mg L^-1 CPPU (N-(2-chloro-4-pyridyl)-N'-phenylurea) application can improve postharvest storage of litchi fruit. In this study, we investigated the improved storability of litchi fruit by CPPU application from the perspectives of fruit maturity and seed vigor. Litchi fruit on the tree were treated with CPPU 2 weeks before commercial maturation. Fourteen days after CPPU application, the treated fruit exhibited 61% higher pericarp chlorophyll, 22% thicker pericarp and 76% lower anthocyanin concentrations than untreated controls, which indicates delayed on-tree fruit maturation. CPPU also remodeled the endogenous hormone profiles in the pericarp and seeds, elevating pericarp IAA and DHZR by 47% and 90%, representing active auxin and cytokinin forms, respectively. During the 12 days of ambient storage of the treated preharvest fruit, CPPU-treated fruit showed reduced pericarp browning, disease incidence, and electrolyte leakage, while maintaining a 72% marketable fruit rate against the control's 25% and higher antioxidant enzyme (APX) activity, indicating an increase in fruit storability when compared to the control. Moreover, CPPU suppressed the upregulation of eight senescence-related genes, including LcLOX1.5-1, LcLOX1.5-2, and LcRNase3. Notably, seed vigor of the litchi fruit decreased with the progress of storage, while the CPPU treatment maintained higher seed vigor compared to the control. These results suggest that the enhanced litchi fruit storability by preharvest CPPU application may be linked to recalcitrant seed vigor maintenance, hormone profile modulation, and pericarp senescence delay.