Mapping the sex determination region in the Salix F₁ hybrid common parent population confirms a ZW system in six diverse species

Within the genus Salix, there are approximately 350 species native primarily to the northern hemisphere and adapted to a wide range of habitats. This diversity can be exploited to mine novel alleles conferring variation important for production as a bioenergy crop, but also to identify evolutionarily important genes, such as those involved in sex determination. To leverage this diversity, we created a mapping population by crossing six Salix species (S. viminalis, S. suchowensis, S. integra, S. koriyanagi, S. udensis, and S. alberti) to common male and female S. purpurea parents. Each family was genotyped via genotyping-by-sequencing and assessed for kinship and population structure as well as the construction of 16 backcross linkage maps to be used as a genetic resource for breeding and selection. Analyses of population structure resolved both the parents and F1 progeny to their respective phylogenetic section and indicated that the S. alberti parent was misidentified and was most likely S. suchowensis. Sex determining regions were identified on Salix chromosome 15 in the female-informative maps for seven of the eight families indicating that these species share a common female heterogametic ZW sex system. The eighth family, S. integra × S. purpurea, was entirely female and had a truncated chromosome 15. Beyond sex determination, the Salix F1 hybrid common parent population (Salix F1 HCP) introduced here will be useful in characterizing genetic factors underlying complex traits, aid in marker-assisted selection, and support genome assemblies for this promising bioenergy crop.