Ancestral origins and genetic diversity of cultivated sunflower: Coancestry analysis of public germplasm

Cultivated sunflower (Helianthus annuus L.) seems to have originated from a small number of ancestral germplasm sources. The number of key ancestors and how much each ancestor has contributed to the genetic diversity of public inbred lines is not known. We used coancestry analysis to assess this. The pedigrees of publicly released inbred lines were traced as far back as possible. Coancestries were estimated among 106 oilseed and 50 confectionery inbred Lines and 157 ancestral germplasm sources. Cluster and principal component analyses of the coancestry matrix separated lines into broad market (oilseed versus confectionery) and fertility restorer (restorer versus maintainer) classes. There were four subgroups among oilseed maintainer lines (B-lines) and three subgroups among oilseed restorer lines (R-lines); however, the R-line subgroups were heterogeneous and the boundaries between them were not sharp. These B and R subgroups may constitute heterotic groups. Sixty-eight percent of oilseed R-line diversity traced to seven germplasm sources, while 73% of oilseed B-line diversity traced to eight germplasm sources. Seventy-three percent of confectionery R-line diversity traced to two germplasm sources, while 65% of confectionery B-line diversity traced to four germplasm sources. The mean coancestry between oilseed R-lines was 0.25, between oilseed B-lines was 0.10, between confectionery R lines was 0.31, and between confectionery B-lines was 0.25; thus, the genetic diversity among oilseed B-lines seems to be wider than among lines within other groups. Pedigree analysis created a nearly complete framework of heterotic groups for public germplasm developed in the USA, even though some lines could not be assigned to heterotic groups because of incomplete pedigree data. By combining pedigree and DNA fingerprint data, a more comprehensive picture of heterotic groups should emerge for cultivated sunflower.