Genetic variation underlying kernel size, shape, and color in two interspecific S. bicolor 2 × S . halepense subpopulations

Throughout the history of sorghum domestication, kernel traits have been subject to extensive selection. Breeding of grain sorghum is highly dependent on kernel morphology, which influences yield and quality. This study examined the genetic variation and architecture of kernel size, shape, and color among two BC 1 F 2 subpopulations, H4 and H6, derived from crossing Sorghum bicolor BTx623 and Sorghum halepense Gypsum 9E. We phenotyped 246 BC 1 F 2 families and their parents in two locations for two years using high-throughput digital imaging techniques, to determine fourteen kernel traits in five broad categories: size (area, length, width, and aspect ratio), shape (circularity and PC1), density (factor form density; FFD), weight (1000-kernel weight) and color (RGB and CIE-L*a*b*). Based on single-trait, interval mapping, we identified 76 and 71 significant QTLs in the H4 and H6 subpopulations, respectively. Both parent genotypes contributed QTL alleles that conferred positive additive effects, indicating that Sorghum halepense contains alleles that may enhance some kernel-related traits of elite sorghums. Some genomic regions affect many traits—for example, a linkage group 6 homolog in the H4 subpopulation was associated with several kernel traits in the region between 0 and 57.3 cM, including FFD, area, length, and width; and in H6 between 56.8 and 185.9 cM contained QTLs associated with kernel color parameters (R, G, L* and B*), FFD, kernel shape (PC1), kernel area, aspect ratio, kernel width, and 1000-kernel weight. These results contribute to a better understanding of genetic factors governing sorghum kernel traits, providing a foundation for improving grain and quality traits in both annual and perennial sorghums using genomic tools.