Maize Genomics and Genetics 2025, Vol.16, No.3, 108-118 http://cropscipublisher.com/index.php/mgg 114 threshold of the number of corn spikelets under high temperature stress, which can provide a basis for breeding and seed selection in nearly half of the world's corn-growing areas. He and Dr. Zhang Yingjun of China Agricultural University conducted precise identification of the backbone corn varieties of different ages in China and the United States, systematically analyzed the evolutionary trends of the male and female ears, yield characteristics and heat resistance of corn germplasm resources, and determined that under high temperature climate stress, the size of the corn male ear is indeed the key to affecting yield, and concluded that high temperature-resistant corn varieties require the number of male spikelets to be ≥ 700 spikelets and flowering to ensure normal pollination of corn and achieve high and stable yields. 6.2 Field trials of heat-tolerant hybrids and their performance evaluation Field trials are an important part of maize heat tolerance research and breeding practice. Through planting and measurement in real agricultural ecological environments, the physiological, agronomic and yield performance of varieties under high temperature stress can be comprehensively evaluated (Longmei et al., 2021; Elmyhun et al., 2024). Li et al. (2024) from the Institute of Botany, Chinese Academy of Sciences, constructed a transcriptome map of maize under heat stress and used co-expression network analysis to identify that the HSF and ERF transcription factor families were highly enriched in the "heat response" module, and further locked in the core heat shock transcription factor ZmHSF20. Functional verification showed that under high temperature stress conditions, the Zmhsf20 mutant had stronger heat resistance than the wild type, while the ZmHSF20 overexpression line showed higher high temperature sensitivity, indicating that ZmHSF20 plays a negative regulatory role in regulating maize heat tolerance (Figure 1). Figure 1 Heat tolerance is modulated by ZmHsf20. A) Construction of CRISPR/Cas9-mediated Zmhsf20 knockout lines (Adopted from Li et al., 2024)
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