Impact of individual and combined water deficit and high temperature on maize seed set: a field study

Drought and heat during flowering critically reduce maize seed set. Current understanding of how these conditions affect pollen release and silk development, which are key determinants of seed set, remains inadequate, particularly under combined water deficit (WD) and high temperature (HT) stresses. This study evaluated the effects of drought and heat on seed set in two maize hybrids, Zhengdan 958 and Demeiya 1, derived from temperate and cool-temperate regions, respectively. These hybrids were exposed to conditions of water deficit, high temperature, and combined water deficit and high temperature (WDHT) within semi-automatic rainout shelters in field ponds, enabling precise simulation of environmental stresses. Relative to controls, seed set in Zhengdan 958 decreased by 32% under WD, 30% under HT, and 41% under combined WDHT conditions. In Demeiya 1, seed set reductions were 26% for WD, 25% for HT, and 34% for WDHT. These reductions were linked to notable decreases in silk fresh weight, pollen weight, and pollen activity. Additionally, the ¹³C content in anthers and the dry matter allocated to tassels decreased by 14.5–53.5% and 3.0–21.0%, respectively. Similarly, the ¹³C content in silks and dry matter allocated to ears decreased by 61.0–91.5% and 14.0–40.0%, respectively. Cross-pollination studies indicated that both hybrids exhibited similar sensitivities to WD and HT; however, silk was more vulnerable under WD and pollen more so under HT in Zhengdan 958, while the reverse was true for Demeiya 1. The combined stresses of WDHT had the most severe effects on both silk and pollen in both hybrids. The observed decreases in seed set under stress conditions were primarily due to limited carbohydrate and dry matter accumulation in reproductive tissues, which impacted silk weight, pollen release, and viability. These findings highlight the critical impact of environmental stresses on the reproductive success of maize, emphasizing the need for strategies to enhance resilience to combined abiotic stresses.