Maize Physiological Responses to Heat Stress and Hormonal Plant Growth Regulators Related to Ethylene Metabolism

Hormonal plant growth regulators (HPGRs) have been evaluated in field grown maize ( Zea mays L.), but never as a tool for prevention or mitigation of heat stress. We analyzed grain yield determination of maize crops exposed to contrasting temperature regimes (nonheated control plots [T C ]; heated plots [T H ]) and the application of HPGRs associated with ethylene metabolism (ethephon [ETH]; MCP [1‐MCP]). Heating extended over daytime hours between V 11 and tasseling (VT), and products were sprayed immediately before (V 11 ) and/or during (V 16 ) heating. Plants treated with ETH always had reduced height (10–21%) and leaf area (3–10%), but these trends usually had no effect on light interception during treatment period. Biomass production was markedly affected by heating, but a significant interaction effect ( P < 0.01) indicated that HPGRs caused (i) no effect among T H plots, and (ii) a decrease (13–19% for ETH and 3.8–9.4% for MCP) among T C plots. The interaction effect computed for grain yield highlighted that ETH had mild negative effects (≤ 18%) among T C plots and large positive effects among T H plots (up to 73%), whereas MCP had no effect among the former and mild positive (V 16 ) or negative (V 11 ) effects among the latter. Variations in grain yield were due to variations in kernel numbers ( r 2 ≥ 0.92), which were explained by ear growth rate around flowering ( r 2 ≥ 0.97). Timely application of HPGRs was critical for improving biomass allocation to the ear (ETH) and having adequate blockage of ethylene receptors (MCP).