Indole-3-acetamide is an efficient alternative to 2,4-dichlorophenoxyacetic acid in citrus postharvest handling

The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) has been extensively applied in citrus postharvest treatment for over six decades to preserve fruit freshness. However, restrictions on its use in the European Union and several Asian countries have necessitated the development of an effective alternative. This study explores the potential of indole-3-acetamide (IAM), an auxin precursor enzymatically converted to active auxin within plant tissues, in mitigating calyx senescence and preserving fruit quality in Satsuma mandarin. After 28 d of storage, calyx senescence rates in IAM and 2,4-D treated fruit were 44 % and 48 %, respectively, both lower than that of the control (65 %). IAM treatment effectively minimized postharvest water loss without compromising total soluble solids (TSS) and titratable acidity (TA) content. Reactive oxygen species (ROS) analysis revealed contrasting effects of IAM on O₂^•- and H₂O₂ levels. Notably, IAM markedly enhanced total phenolic and flavonoid accumulation during the early storage phase and promoted lignin biosynthesis in the later stage. Additionally, IAM-treated fruit exhibited elevated levels of key primary metabolites, including proline, asparagine, threonine, phenylalanine, and sucrose, compared to the control. The efficacy of IAM in delaying calyx senescence was further validated in Newhall navel orange and Olinda Valencia orange, underscoring its potential as a viable alternative to 2,4-D in citrus postharvest management.