| Sumario: | The two main factors contributing to heat stress are higher temperatures and low relative humidity at high temperatures. Growing almost year-round, maize crops in the lowland tropics are exposed to rising temperatures, negatively affecting crop productivity, especially under rainfed conditions. Studies have identified several morphological, biochemical, and physiological changes in field crops, including maize under heat stress. Among these, a few changes enable plants to adapt to heat stress (stress-adaptive traits), while others exhibit adverse effects of stress (stress-responsive traits). At the biochemical level, heat stress results in increased levels of superoxide dismutase (SOD) and catalase enzyme activities in cells, as well as elevated levels of Heat Shock Proteins (HSPs). Options have been identified to mitigate the effects of heat stress on maize crops, such as suitable planting time to avoid a high-temperature regime coinciding with critical crop growth stages, furrow sowing, and frequent irrigation to maintain a vital minimum relative humidity in the air. Efforts on genetic improvement for heat tolerance in maize resulted in the development of new heat-tolerant maize hybrids, which can thrive at temperatures beyond threshold limits for tropical maize and suffer relatively less under heat stress. However, the challenge remains mainly due to low genotypic variability for stress in elite maize germplasm and strong genotype-by-environment interaction under heat stress, resulting from varying vapor pressure deficits (VPD) at high temperatures. Therefore, diving deeper and exploring local landraces and wild accessions is necessary to explore wider genotypic variation for heat stress tolerance in tropical maize. Recent advances in genomics-assisted breeding may help identify genomic regions associated with heat stress tolerance in maize and target the introgression of validated genomic regions into elite maize germplasm to develop the next generation of maize cultivars with improved, stable performance under heat stress conditions. In this article, we reviewed the progress and key findings on various aspects of research on heat stress in field crops, with an emphasis on tropical maize, which may help refine the approaches of research programs working on heat stress and aiming to develop crop varieties with improved tolerance to heat stress.
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