Endogenous Hormones Improve Lodging Tolerance of Maize (Zea mays L.) by Regulating Stalk Structure Under Elevated Temperature

Global warming is an irreversible trend. Maize hybrids responded differently to elevated temperature throughout the whole growth periods, but the underlying mechanisms are unclear, particularly from the early stalk growth stage that is used to adapt different environments. For this, two hybrids, Zhengdan958 (heat-tolerant hybrid) and Xianyu335 (heat-sensitive hybrid), including control (CK), the whole growth period increased by 2 °C  (CK+2°C), and the whole growth period increased by 4 °C (CK+4°C). Compared to CK, the length of the third internode of CK+2°C and CK+4°C at 56 days after planting (DAP), increased on average by 6.91% and 19.20%, respectively. The elongation of internode in XY335 grew faster than in ZD958, and the third internode density of XY335 decreased more than that of ZD958 at 28 DAP. With temperature increasing, cell length elongated significantly, and cell layers decreased significantly under the CK+4°C and CK+2°C. Compared with CK, the total width of ground tissue cells, hypodermis cells and epidermis cell width of CK+4°C and CK+2°C decreased by 26.16%, 30.29%, 28.82%, and 18.57%, 24.39%, 17.11%, respectively. The major axe (R1), minor axe (R2), and length of the third internode were correlated negatively with ratios of IAA/ABA, ZR/ABA, and GA3/ABA. There was significantly positive relationship between total width of ground tissue cells and crushing strength, thrust resistance (p < 0.05). And the correlations between crushing strength and thrust resistance (p < 0.05), R1 cell layers and R2 cell layers (p < 0.01) was significantly positive. This finding would supply a reference to evolve strategies in breeding stress-tolerant hybrids under the global climate change.