The da1 mutation in wheat increases grain size under ambient and elevated CO(2) but not grain yield due to trade‐off between grain size and grain number

Grain size is potentially yield determining in wheat, controlled by the ubiquitin pathway and negatively regulated by ubiquitin receptor DA1. We analyzed whether increased thousand grain weight in wheat da1 mutant is translated into higher grain yield and whether additional carbon provided by elevated (e)CO(2) can be better used by the da1, displaying higher grain sink strength and size. Yield‐related, biomass, grain quality traits, and grain dimensions were analyzed by two‐factorial mixed‐model analysis, regarding genotype and eCO(2). da1 increased grain size but reduced spikes and grains per plant, grains per spike, and spikelets per spike, independent of eCO(2) treatment, leaving total grain yield unchanged. eCO(2) increased yield and grain number additively and independently of da1 but did not overcome the trade‐off between grain size and number observed for da1. eCO(2) but not da1 impaired grain quality, strongly decreasing concentrations of several macroelement and microelement. In conclusion, intrinsic stimulation of grain sink strength and grain size, achieved by da1, is not benefitting total yield unless trade‐offs between grain size and numbers can be overcome. The results reveal interactions of yield components in da1‐wheat under ambient and eCO(2), thereby uncovering limitations enhancing wheat yield potential.