Association mapping of brassinosteroid candidate genes and plant architecture in a diverse panel of Sorghum bicolor.

KEY MESSAGE: This first association analysis between plant architecture and BR candidate genes in sorghum suggests that natural allelic variation has significant and pleiotropic effects on plant architecture phenotypes. Sorghum bicolor (L) Moench is a self-pollinated species traditionally used as a staple crop for human consumption and as a forage crop for livestock feed. Recently, sorghum has received attention as a bioenergy crop due to its water use efficiency and biomass yield potential. Breeding for superior bioenergy-type lines requires knowledge of the genetic mechanisms controlling plant architecture. Brassinosteroids (BRs) are a group of hormones that determine plant growth, development, and architecture. Biochemical and genetic information on BRs are available from model species but the application of that knowledge to crop species has been very limited. A candidate gene association mapping approach and a diverse sorghum collection of 315 accessions were used to assess marker-trait associations between BR biosynthesis and signaling genes and six plant architecture traits. A total of 263 single nucleotide polymorphisms (SNPs) from 26 BR genes were tested, 73 SNPs were significantly associated with the phenotypes of interest and 18 of those were associated with more than one trait. An analysis of the phenotypic variation explained by each BR pathway revealed that the signaling pathway had a larger effect for most phenotypes (R (2) = 0.05-0.23). This study constitutes the first association analysis between plant architecture and BR genes in sorghum and the first LD mapping for leaf angle, stem circumference, panicle exsertion and panicle length. Markers on or close to BKI1 associated with all phenotypes and thus, they are the most important outcomes of this study and will be further validated for their future application in breeding programs.