Ethephon Treatment Enhanced Postharvest Litchi Fruit Resistance to Peronophythora litchii by Strengthening Antioxidant Capacity and Defense Systems

Litchi downy blight, caused by <i>Peronophythora litchii</i>, is a major postharvest disease that leads to severe pericarp browning and fruit decay, significantly reducing market quality. Strengthening the fruit's innate defense systems represents a promising strategy for minimizing these losses. This study investigated the efficacy and underlying mechanisms of ethephon treatment in controlling postharvest litchi downy blight. The results showed that treatment with 400 mg·L^-1 ethephon solution via a 2-min immersion significantly suppressed <i>P. litchii</i> infection, reduced the disease index and pericarp browning index, and enhanced the rate of ethylene production. Ethephon application notably increased 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, and the activities of key antioxidant and defense-related enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), chitinase (CHI), β-1,3-glucanase (GLU), and phenylalanine ammonia lyase (PAL). Concurrently, it up-regulated the expression of corresponding genes <i>LcCAT</i>, <i>LcAPX</i>, <i>LcCHI</i>, <i>LcGLU</i>, <i>LcPAL</i>. In contrast, ethephon treatment reduced the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). In summary, ethephon treatment suppresses postharvest litchi downy blight likely through the enhancement of both antioxidant and pathogen defense capacities. These findings provide valuable insights into the potential application of ethephon for maintaining postharvest quality in litchi fruit.