Maintenance breeding and breeding for yield potential both contribute to genetic improvement in wheat yield

Studies that quantify the contribution of genetic improvement to crop yields typically rely on comparisons of old cultivars grown side-by-side with more recent ones. This approach, however, does not allow to distinguish gains in yield potential versus maintenance breeding that aims to keep cultivars adapted to the evolving biophysical environment, including pests, diseases, and climate. Here we show an overall wheat yield improvement of 73 kg ha-1 y-1 based on direct comparison of modern cultivars against older ‘check’ cultivars using data from multi-environment trials from Argentina, France, United Kingdom, and United States. However, almost half of this improvement (33 kg ha-1 y-1) is attributable to maintenance breeding needed to counteract the yield erosion of older cultivars, and the other portion (40 kg ha-1 y-1) can be associated with the higher yield potential of modern cultivars. We conclude that comparison of new versus old cultivars under current conditions leads to an overestimation of genetic gains in yield potential. Current crop variety trials typically compare new varieties with older checks. Using publicly available wheat trial data, the authors show that much of the yield gain attributed to new varieties actually stems from the declining adaptability of older cultivars to changing environments.