Novel grain weight loci revealed in a cross between cultivated and wild sorghum

Core Ideas: •Quantitative trait loci for thousand grain weight were mapped in a cross between domesticated and wild sorghum. •The majority of thousand grain weight quantitative trait loci were negatively associated with grain number. •Novel large-effect thousand grain weight quantitative trait loci possibly related to sorghum domestication were identified. •Candidate genes with domestication signal were identified within the large-effect quantitative trait loci. Abstract: Grain weight has increased during domestication of cereals. Together with grain number it determines yield, but the two are often negatively correlated. Understanding the genetic architecture of grain weight and its relationship with grain number is critical to enhance crop yield. Sorghum is an important food, feed, and biofuel crop well-known for its adaptation to drought and heat. This study aimed to dissect the genetic basis of thousand grain weight (TGW) in a BC1F5 population between a domesticated sorghum accession and its wild progenitor, Sorghum bicolor subsp. verticilliflorum, and investigate its relationship with grain number. Thousand grain weight, grain number, and yield were measured in field trials in two successive years. A strong negative correlation between TGW and grain number was observed in both trials. In total, 17 TGW quantitative trait loci (QTL) were identified, with 11 of them exhibiting an opposing effect on grain number, implying the correlation between TGW and grain number is due to pleiotropy. Nine grain size candidate genes were identified within 6 TGW QTL, and of these 5 showed signatures of selection during sorghum domestication. Large-effect QTL in this study that have not been identified previously in cultivated sorghum were found to contain candidate genes with domestication signal, indicating that these QTL were affected during sorghum domestication. This study sheds new light on the genetic basis of TGW, its relationship with grain number, and sorghum domestication.