Cuticular wax composition and postharvest changes in 74 avocado accessions: Links to fruit water loss and biphasic effects of wax constituents on Colletotrichum siamense growth

Fruit cuticular wax serves as an important barrier against postharvest deterioration. However, knowledge of its composition, postharvest changes, and biological functions in avocado remains limited. Here, we performed a large-scale characterization of fruit cuticular wax composition and diversity across 74 avocado accessions at harvest and ripe stages, investigated the associations of wax traits with fruit water loss, and evaluated the effects of representative wax constituents on fungal growth. A total of 20 wax constituents belonging to six chemical classes were identified, including five alkanes, two aldehydes, three fatty acids, five alcohols, three tocopherols, and two sterols. Alkanes, particularly C27 and C29 homologs, were the dominant wax components in most accessions. Between the harvest and ripe stages, total cuticular wax content generally increased across the 74 avocado accessions, with mean wax content rising from 13.84 to 18.06 μg·cm⁻², primarily driven by alkane accumulation. Partial correlation analysis showed negative associations between aliphatic wax components and fruit water loss, with alkanes showing the strongest associations. In contrast, sterols (cyclic wax components) showed a weak positive association with water loss. In vitro assays further demonstrated that representative cuticular wax constituents, including alkanes, alcohols, sterols, and tocopherols, exhibited concentration-dependent biphasic effects on the mycelial growth of Colletotrichum siamense , with stimulation at low concentrations and inhibition at high concentrations. These findings provide new insights into the diversity of avocado cuticular wax composition across a large accession panel and the potential biological roles of wax components during postharvest ripening.