High temperature stress in chrysanthemum: developmental impacts, associated hydraulic and ionic constraints, and adaptive responses

Abstract

High temperature is a major environmental constraint limiting the growth, development, ornamental quality, and reproductive performance of chrysanthemum (Chrysanthemum morifolium). In production systems, thermal stress often coincides with drought-like hydraulic stress, including increased vapor pressure deficit and soil water deficit, and may promote salinity or ionic stress under specific substrate, fertigation, or protected-cultivation conditions. These associated constraints may intensify high-temperature-induced developmental disorders, but their relative importance depends on cultivar, developmental stage, and cultivation context. In this review, we synthesize current knowledge of high-temperature responses in chrysanthemum, with an emphasis on developmental vulnerability and species-specific ornamental traits. We first summarize the effects of elevated temperature on vegetative growth, adventitious rooting, photosynthesis, plant architecture, flowering time, capitulum morphogenesis, floral pigmentation, postharvest performance, pollen fertility, and seed set. We then discuss how heat-responsive pathways intersect with water-status regulation, ion homeostasis, hormone signaling, reactive oxygen species metabolism, heat shock responses, transcriptional regulation, and epigenetic modulation. Particular attention is given to distinguishing direct evidence from chrysanthemum from mechanistic insights inferred from model plants or other crops. Finally, we outline adaptive strategies, including environmental control, chemical priming, grafting, germplasm evaluation, molecular breeding, and AI-assisted cultivation. This review provides a high-temperature-centered framework for understanding stress-associated developmental disorders in chrysanthemum and for guiding the future improvement of climate-resilient ornamental cultivars.