The genetics of branching in sunflower

Shoot branching played an important role in domestication of modern cultivated sunflower. Cultivated sunflowers are unbranched and originated from strongly branched wild populations distributed throughout North America. Branching plays an important role in hybrid sunflower seed production where an unbranched, sterile male line is crossed with a fertile branched line exhibiting indeterminate flowering that increases the window for hybridization. A single recessive B locus located in linkage group 10 has been shown to control branching in domesticated sunflower. In addition, several other small effect quantitative trait loci (QTLs) have been identified throughout the sunflower genome suggesting that branching is a complex trait that is most likely controlled by several different genes. With the aim of identifying multiple QTLs associated with branching, we screened an association mapping population comprising of 288 lines developed in our lab which captures 90% diversity of cultivated sunflower. This population was phenotyped for different kinds of branching such as apical, mid and basal branching in three different field locations (Georgia and Iowa in North America and British Columbia, Canada). This population was genotyped on a 10K Illumina single nucleotide polymorphism (SNP) array. Association of 5566 SNPs with various branching traits was analyzed using mixed linear model method in TASSEL which account for both population structure and kinship. In addition to detecting previously identified QTLs, we also found several new loci associated with branching.