Responses of Sweet Maize ( <scp> <i>Zea mays</i> </scp> L.) Yield and Kernel Quality to High‐Temperature Seasons in South China

ABSTRACT High temperatures impact sweet maize production; however, their specific effects on grain yield and kernel quality across different growing seasons remain unquantified. This study investigated high‐temperature season effects, evaluated the yield and kernel quality responses in two sweet maize hybrids with different heat tolerance, and analysed the response mechanisms of dry matter accumulation (DMC), flowering, and grain filling in South China. Two contrasting sweet maize hybrids were planted annually in spring, summer, and autumn over a 2‐year field experiment in Guangdong, South China. An evaluation of extreme degree days at different growth stages revealed that the sweet maize crops experienced high‐temperature stress during their reproductive stages in the spring and summer growing seasons. In the high‐temperature season, ‘HMT8’ showed heat sensitivity, with the grain yield significantly decreasing because of the lower kernel weight. The reduced grain‐filling rates, especially in the early stages, contributed to lower kernel weight, which may be related to the decreased leaf area index (LAI) and post‐anthesis DMC. Comparatively, ‘GLT27’ was heat‐tolerant, with the grain yield slightly increasing because of the increased kernel number. However, it appeared cold‐sensitive during the grain‐filling stages in autumn. ‘GLT27’ exhibited stable or slightly increased pollen viability, LAI, post‐anthesis DMC, and grain‐filling rates. Furthermore, both hybrids showed reduced sucrose and elevated free amino acid content in the high‐temperature seasons. Early grain‐filling and post‐anthesis DMC rather than reproductive organ viability may limit sweet maize during high‐temperature seasons. Managing crops by selecting varieties and cultivation practices for different annual growing seasons is crucial.