Association Mapping for Plant Architecture Traits Related to Brassinosteroids in a Diverse Sorghum Bicolor Collection.

Sorghum bicolor (L) Moench is a cultivated and self-pollinated species used for human consumption, livestock feed, forage and bio-energy production. Sorghum presents a remarkable diversity in the species bicolor that can be exploited to identify new genes associated with traits of interest. Recently, sorghum has received attention as a bioenergy crop because of its water use efficiency, yield biomass potential and biomass composition.  To develop superior sorghum inbred lines for bioenergy production, it would be beneficial to understand the genetic mechanisms controlling plant architecture traits. Brassinosteroids (BRs) are steroid hormones that control different aspects of plant growth and development, and are directly associated with the control and regulation of important plant architecture traits. Brassinosteroid biosynthesis and signaling pathways have been studied in model species such as Arabidopsis, rice and maize, but not in sorghum. In the present study, candidate gene association mapping and a diverse sorghum collection of 333 accessions were used to assess marker-trait associations between brassinosteroid biosynthesis and signaling genes and eight plant architecture traits. Phenotypic data for plant height, leaf angle, stem circumference, flowering time, panicle exertion, panicle length, number of tillers, and number of internodes was collected in three locations in Iowa in 2010 and 2012. Several SNPs in BR candidate genes were significantly associated with the phenotypes of interest, confirming the genetic complexity of the traits. This project has the ultimate goal of understanding the effect of brasinosteroids on sorghum plant architecture and to develop molecular tools that can be used in breeding programs to improve sorghum lines for biofuel production.