Rate of photosynthetic induction in fluctuating light varies widely among genotypes of wheat

Crop photosynthesis and yield are limited by slow photosynthetic induction in sunflecks. We quantified variation in induction kinetics across diverse genotypes of wheat for the first time. In a preliminary study using penultimate leaves of 58 genotypes grown in the field, we measured induction kinetics for maximum assimilation rate ( A max ) after a shift from full darkness to saturating light (1700 μmol m -2 s -1 ) with 1-4 replicates per genotype. We then grew 10 of these genotypes with contrasting responses in a controlled environment and quantified induction kinetics of carboxylation capacity ( V cmax ) from dynamic A vs c i curves after a shift from low to high light (50 to 1500 μmol m -2 s -1 ), with 5 replicates per genotype. Within-genotype median time for 95% induction (t 95 ) varied from 8.4 to 23.7 min across genotypes for A max in field-grown penultimate leaves, and from 6.7 to 10.4 min for V cmax in chamber-grown flag leaves. Our simulations suggested that non-instantaneous acclimation reduces daily net carbon gain by up to 16%, and that breeding to speed up V cmax induction in the slowest genotype to match that in the fastest genotype could increase daily net carbon gain by more than 4%, particularly for leaves that experience predominantly short-duration sunflecks.