Improving wheat productivity reveals an emerging yield gap associated with short-term change in atmospheric humidity

Few studies have evaluated the effect of humid weather on wheat productivity and yield gaps. Humid weather conditions before, during, and after flowering cause losses associated with Fusarium head blight and pre-harvest sprouting. To increase the actual yield, efforts such as ensuring that farm yield is commensurate with yield potential via wheat breeding activities have been made in the wake of increasingly adverse climatic conditions. In the present study, the time-series wheat yield gap (simulated yield potential minus actual on-farm yield) was analyzed for the 1984-2020 period in the humid region of northern Japan, where major varieties have been replaced with more productive (high yield, preharvest resistant, and Fusarium head blight-resistant) ones almost every decade. The periodical introduction of alternative varieties has altered the meteorological factors responsible for yield gaps. Older varieties, 'Chihoku-komugi' and 'Hokushin,' exhibited higher sensitivity to atmospheric humidity before harvest and after the heading period. A new high-yield variety, 'Kitahonami,' with increased floret numbers, reduced the periodical mean yield gap from 1.95 Mg/ha to 1.14 Mg/ha, whereas the yield gap often expanded under vapor pressure deficit of < 0.3 kPa during the flowering period. The results indicated that 'Kitahonami' yield potentially depends on the yield rate of potential fertile florets, which leads to its vulnerability to short-term rainy, humid weather during the flowering period. Current breeding strategies reduce humidity damage at sensitive duration of preharvest sprouting-resistant, and Fusarium head blight-resistant, while the emerging yield gap factors continue to reflect the traits that could be targeted for improvement.