Immediate and lasting effects of heat or water stress on summer tropical maize lines and derived hybrids

Abstract

Maize crops are exposed to heat stress, water restrictions, or combined stress during vegetative stages, which can immediately limit crop growth and extend into the flowering period, affecting grain yield. This study evaluated the effects of individual and combined episodes of heat and water stress on (i) crop growth rate, daily radiation interception, and radiation use efficiency during the vegetative period and the flowering period, and (ii) crop grain yield. In controlled field experiments, temperature and water regimes were adjusted over three summer seasons from the nine to seventeen-ligulated leaf stages (15 days before tasseling). Five genotypes were cultivated, including two white maize hybrids previously classified as tolerant to water stress (H1) or combined heat and water stress (H2), along with their three parental lines from CIMMYT. Individual heat and water stress during vegetative stages reduced crop growth by 28.6% in both hybrids, while combined heat and water stress had the greatest impact on H2 (-33.8%). Variations in crop growth rates were positively associated with the effect of both stresses with radiation use efficiency (r2=0.96) and, to a lesser extent, with daily radiation interception (r2=0.75). Variations in radiation use efficiency were related to canopy temperature, which differed between water-stressed and no-water-stressed crops. Stresses did not affect the crop growth rates of parental lines. At flowering, growth rates of previously stressed crops were reduced (~ -21.7%) but did not result in grain yield penalties. The experimental approach, including maize hybrids and their parental lines, demonstrated the effects of heat and water stress during the vegetative stages. Reductions in crop growth rate were mainly due to the negative impact on radiation use efficiency due to high canopy temperatures. However, these effects were attenuated during the critical period for kernel setting, suggesting no grain yield penalties for summer maize hybrids exposed to individual and combined heat and water stress during vegetative stages.