Phytohormonal Control and Crosstalk in Litchi Fruit Development, Ripening, Abscission and Quality Regulation

Litchi (Litchi chinensis Sonn.) is a commercially important non-climacteric fruit crop whose fruit development, maturation, abscission, and postharvest quality are carefully controlled by a complex network of phytohormones. Unlike climacteric fruits, litchi ripening is predominantly controlled by abscisic acid (ABA) and sugar signaling, with ethylene playing an important role in fruit abscission, senescence, and postharvest degradation. This chapter summarizes current knowledge of main hormone roles in litchi fruit physiology, including ethylene, ABA, jasmonates, brassinosteroids, and salicylic acid. Ethylene regulates abscission by activating cell wall-degrading enzymes and leads to pericarp browning and senescence when in storage. In contrast, ABA is a key regulator of fruit maturity, boosting anthocyanin accumulation, sugar transport, and ripening commencement. New research emphasizes the role of hormonal crosstalk, including auxin-ethylene antagonism, ABA-sugar synergy, and ABA-ethylene interaction, in influencing fruit retention, ripening process, and stress responses. Jasmonates, brassinosteroids, and salicylic acid improve stress tolerance, defense mechanisms, and postharvest quality.Despite these advancements, some crucial research gaps remain. The molecular basis of hormone signaling and crosstalk is still poorly known, especially in terms of gene regulatory networks and functional validation of important genes. Limited integration of multi-omics techniques limits our understanding of ripening and stress physiology. Furthermore, the effects of minor hormones are understudied, and hormonal control throughout postharvest stages, particularly the mechanisms behind pericarp browning, warrants greater exploration. There is also a dearth of standardized, cultivar-specific protocols for applying plant growth regulators (PGRs), as well as insufficient research on genotype-specific responses and the effects of climatic change on hormonal balance. Bridging the gap between laboratory research and field-based applications remains a significant problem.Future research that incorporates modern multi-omics technologies, precise hormonal manipulation, and climate-resilient tactics will be critical for increasing productivity, improving fruit quality, and assuring sustainable litchi farming.