Dissecting the Genetic Basis of Seed Size in Sorghum bicolor

The grasses, including the major cereals wheat, barley, maize, rice and sorghum, are the most agronomically and economically important species, collectively feeding over two thirds of the world population. Amongst the cereals, sorghum which is a staple food for over 500 million people in the semi-arid tropics of Africa and Asia, in addition to being an important source of feed for livestock, is one of the best adapted to drought and high temperatures, and will play an increasingly important role in meeting the challenges of feeding the world’s growing population. Seed size is a major quality attribute and an important determinant of yield that is regulated by a function of potential maximum seed size and the plant’s capacity to fill it. Understanding the genetic basis of seed size in sorghum is of fundamental importance to meet future productivity requirements. In this study, genome-wide association study (GWAS) was performed to dissect the genetic architecture of seed size using two complementary populations, a diversity panel consisting of 900 genotypes and a BC-NAM population consisting of 1400 progeny. A high throughput phenotypic evaluation pipeline was established to measure seed size parameters including thousand seed weight, seed volume, seed length, seed width and seed thickness of these two populations across three locations and two years. In addition to actual seed size, potential maximum seed size achieved through removing half a head during flowering was also evaluated. Genomic regions associated with seed size, genetic potential of seed size and the capacity to fill seed were identified, and candidate genes in these region were identified. Signatures of purifying selection were also detected in key candidate genes. The identification of seed size QTL and candidate genes presents new opportunities for manipulating seed size and ultimately yield in breeding practice.