Maize breeding for smaller tassels threatens yield under a warming climate

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. By comparing the responses of 323 elite maize lines from different breeding eras, the authors demonstrate that reduced tassel size in newer lines can lead to increased susceptibility to high temperature. This highlights the potential for traits optimized by breeding to lead to climate maladaptation.