Variation in seed protein concentration and seed size affects soybean crop growth and development

Abstract

Developing high protein (HP) cultivars is often precluded by the inverse relationship between protein and yield. We hypothesized that attaining HP concentration based on contrasting seed size impacts crop growth and development differently. We screened 97 soybean genotypes and found lines with HP concentration (~450 g kg−1) associated with (i) increased protein content (mg seed−1) in large seed genotypes, and (ii) reduced oil and carbohydrate contents in small seed ones. Then, we evaluated different growth traits in a subset of three HP large and three HP small seed genotypes, as well as in three high-yielding genotypes with average seed size and protein concentration. High-yielding genotypes showed higher leaf area duration and harvest index when compared with HP genotypes, regardless of seed size. High protein large seed was associated with more assimilate availability per seed during seed filling, while HP small seed showed higher leaf area at the beginning of seed fill, more canopy biomass production, and very low levels of assimilate per seed. Results show that selecting for seed protein concentration can impact crop growth and development differently, depending on the strategy used for selection in terms of seed size. These findings, if utilized for parental selection, might contribute to eliminating negative correlations between seed protein and yield, since these strategies may be under different genetic control and/or determine different biophysical constraints.