Genomic Analysis of a Sorghum NAM Population and High Resolution Mapping of Flowering Time

Sorghum genomics research has advanced significantly over the past decade and is making routine marker assisted selection possible in breeding programs. Whereas bi-parental populations lead to the detection of major QTLs and association studies showed better resolution, the Nested Association Mapping design that consists in a joint analysis of reshuffled differentiated genomes is a great compromise between allelic diversity coverage, high resolution and limited false positives. A NAM population was designed at Kansas State University. Ten founders covering sorghum geographic, racial, phenotypic diversity and 75 % of the allelic diversity found in the Sorghum Association Panel were crossed to the common parent Tx430. Recombinant inbred lines (RILs) were derived by single seed descent for 8 generations without selection. In total, 2400 RILs were genotyped with genotyping-by-sequencing SNP markers using ApeKI restriction enzyme. Preliminary analyses were done using 100 000 markers that were polymorphic in at least one population. Both known QTLs as well as new major QTLs were detected for flowering time and plant height. For flowering time, a major adaptive trait in plants, the total polygenic variance explained was 65%. Those results are promising for deciphering the architecture of complex adaptive, quality and yield traits, for both forage and grain sorghum, thanks to high-throughput phenotyping and genotyping.

Keywords: flowering time, height, Sorghum, Nested Association Mapping, Genotyping By Sequencing