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

ABSTRACT 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 [TC]; heated plots [TH]) and the application of HPGRs associated with ethylene metabolism (ethephon [ETH]; MCP [1‐MCP]). Heating extended over daytime hours between V11 and tasseling (VT), and products were sprayed immediately before (V11) and/or during (V16) 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 TH plots, and (ii) a decrease (13–19% for ETH and 3.8–9.4% for MCP) among TC plots. The interaction effect computed for grain yield highlighted that ETH had mild negative effects (≤ 18%) among TC plots and large positive effects among TH plots (up to 73%), whereas MCP had no effect among the former and mild positive (V16) or negative (V11) effects among the latter. Variations in grain yield were due to variations in kernel numbers (r2 ≥ 0.92), which were explained by ear growth rate around flowering (r2 ≥ 0.97). Timely application of HPGRs was critical for improving biomass allocation to the ear (ETH) and having adequate blockage of ethylene receptors (MCP).