Melatonin-mediated mitigation of waterlogging stress in waxy maize: A time-dependent regulation of root architecture, dry matter partitioning and yield

Global warming intensifies extreme rainfall in the Huang-Huai-Hai Plain, threatening waxy maize production while effective mitigation strategies remain limited. Melatonin, a multifunctional plant regulator, shows promise in enhancing stress tolerance, but its efficacy under waterlogging in waxy maize remains unclear. The objectives of this study were to evaluate the yield response of waxy maize to different waterlogging durations and to explore the mitigation potential of exogenous melatonin (MT) under varying intensities of waterlogging stress. Over 2019–2020, a 10-day waterlogging at tasseling reduced fresh ear yield of SKN1 and SKN602 by 17.4% and 17.8% ( P < 0.05). In 2022, JKN2000 was subjected to 0–10 days of waterlogging at tasseling, with or without 100 μmol L⁻ 1 melatonin applied at the V6 stage. Results showed that 8- and 10-day waterlogging reduced fresh ear yield by 10.2% and 11.6%, respectively ( P < 0.05). Melatonin increased yield by 8.2% under 8-day waterlogging. Root growth peaked at 8 days but declined thereafter. Melatonin promoted fine root (<1 mm) formation under 2–6 days of waterlogging and enhanced stem strength under prolonged stress. Dry matter partitioning to the ear increased with melatonin under moderate stress (2–6 days). Our findings demonstrate that exogenous melatonin can mitigate yield loss in waxy maize under short- to medium-term waterlogging (≤8 days) by improving root architecture, stem strength, and assimilate allocation to ears, with a defined efficacy window critical for practical application. • Waterlogging redirected dry matter and nutrient allocation toward roots in maize. • Exogenous melatonin promoted root growth of waxy maize under 2–6 d waterlogging. • Exogenous melatonin enhanced stem mechanical resistance under waterlogging stress. • Exogenous melatonin increased root dry matter and nutrient accumulation under waterlogging.