Dhananjay Gotarkar, Anthony Digrado, Yu Wang, Lynn Doran, Ignacio Sparrow-Munoz, Sarah Chung, Nicholas Lisa, Farwah Wasiq, Gerardo Amaro, Bethany Blakely, Brian W. Diers, Daniel J. Eck and Steven J. Burgess

Improving the efficiency of crop photosynthesis has the potential to increase yields. Genetic manipulationshowed photosynthesis can be improved by speeding up the relaxation of photoprotective mechanisms dur-ing sun-to-shade transitions. However, it is unclear if natural variation in the relaxation ofnon-photochemical quenching (NPQ) can be exploited in crop breeding programs. To address this issue, wemeasured six NPQ parameters in the 40 founder lines and common parent of a Soybean Nested AssociationMapping (SoyNAM) panel over two field seasons in Illinois. Leaf disks were sampled from plants grown inthe field, and induction and relaxation of NPQ were measured under controlled conditions. NPQ parametersdid not show consistently variable trends throughout development, and variation between sampling dayssuggests environmental impacts on NPQ dynamics. Seventeen genotypes were found to show small butconsistent differences in NPQ relaxation kinetics relative to a reference line, providing a basis for futuremapping studies. Finally, a soybean canopy model predicted available phenotypic variation could result in a1.6% difference in carbon assimilation when comparing the fastest and slowest relaxing NPQ values. Nocorrelation could be found between yield and rates of NPQ relaxation, but a full test will require an analysisof isogenic lines