Foliar urea sprays induce budbreak in peach via rapid non-structural carbohydrate metabolism – A lower-toxicity alternative to hydrogen cyanamide

Warm winters in subtropical regions often result in insufficient winter chill accumulation, leading to the unsatisfied chilling requirements in deciduous fruit crops, disrupting budbreak and reducing yield. Hydrogen cyanamide (HC) is the most effective commercial bud-breaking agent, but it poses safety and regulatory concerns. This study evaluated whether foliar urea sprays could serve as a lower-toxicity alternative to HC. We provide the first integrated assessment of non-structural carbohydrate (NSC) dynamics in both stem and root tissues following the chemical induction of budbreak. One-year-old potted ‘Tainung No. 7 HongLing’ peach (Prunus persica L.) trees grown in central Taiwan were treated with sprays of foliar urea (14 % and 20 %, w/v), HC (0.5 % and 1 %, v/v), or water (untreated control) on December 7 and 23 2022. We assessed treatment effects on defoliation, budbreak, dry weight distribution, and NSC concentrations in stems and roots. HC and foliar urea sprays effectively accelerated defoliation and budbreak compared to the untreated control. The HC treatment maintained stable NSC concentrations in stems and accumulated starch in roots, suggesting a more conservative resource-use strategy. In contrast, foliar urea sprays resulted in a pronounced depletion of glucose, fructose, and starch in both stems and roots, indicating strong carbon mobilization. Despite these differences, both treatments significantly increased dry weights of new shoot flushes, indicating successful bud dormancy release supported by internal carbon reserves. These findings suggest that foliar urea sprays are an effective and safer alternative to HC for dormancy release in low-chill peach. However, its use should be carefully managed to avoid long-term stress from carbon reserve depletion. This study provides physiological insights to guide the development of safer and more sustainable bud-breaking strategies under climate-induced chilling limitations.