Variation in relaxation of non-photochemical quenching between the founder genotypes of the soybean (Glycine max) nested association mapping population

Improving the efficiency of crop photosynthesis has the potential to increase yields. Genetic manipulation showed photosynthesis can be improved by speeding up the relaxation of photoprotective mechanisms during sun-to-shade transitions. However, it is unclear if natural variation in the relaxation of non-photochemical quenching (NPQ) can be exploited in crop breeding programs. To address this issue, we measured six NPQ parameters in the 40 founder lines and common parent of a Soybean Nested Association Mapping (SoyNAM) panel over two field seasons in Illinois. Leaf disks were sampled from plants grown in the field, and induction and relaxation of NPQ were measured under controlled conditions. NPQ parameters did not show consistently variable trends throughout development, and variation between sampling days suggests environmental impacts on NPQ dynamics. Seventeen genotypes were found to show small but consistent differences in NPQ relaxation kinetics relative to a reference line, providing a basis for future mapping studies. Finally, a soybean canopy model predicted available phenotypic variation could result in a 1.6% difference in carbon assimilation when comparing the fastest and slowest relaxing NPQ values. No correlation could be found between yield and rates of NPQ relaxation, but a full test will require an analysis of isogenic lines.