Breeding programmes have increased the yields of major crops, including maize (Zea mays L.), but the suitability of optimized traits to future climates remains unclear. Here, by comparing the responses of 323 elite maize inbred lines from different breeding eras under natural field conditions, we show that while newer lines exhibit higher grain yield than the early released lines under standard growth, the bred trait of reduced tassel size increases the susceptibility of newly released lines to high temperature during flowering. We identified a potential threshold for spikelets per tassel (~700), over which maize can produce a stably high seed set ratio under warm conditions, and show that small-tassel (<700 spikelets per tassel) genotypes are now unsuitable in 23.7% of global maize-growing regions. Our work highlights the need to consider possible climate change maladaptation resulting from breeding programmes.

育种计划提高了包括玉米 （Zea mays L.） 在内的主要作物的产量，但优化性状对未来气候的适用性仍不清楚。在这里，通过比较不同育种时代的 323 个优质玉米自交系在自然田间条件下的响应，我们表明，虽然在标准生长下，较新的品系比早期释放的品系表现出更高的产量，但穗子尺寸减小的育种性状增加了新释放品系在开花期间对高温的敏感性。我们确定了每个抽穗的小穗的潜在阈值 （~700），超过该阈值，玉米可以在温暖的条件下产生稳定的高结实率，并表明小穗（每个穗 <700 个小穗）基因型现在在全球 23.7% 的玉米种植区不合适。我们的工作强调需要考虑育种计划可能导致的气候变化适应不良。