Assembly and annotation of eleven Salix (shrub willow) genomes

The shrub willows (Salix section Vetrix) are an emerging bioenergy crop in North America and Eurasia. However, genomics resources in this section are still quite limited, with only a few reference genomes available, despite many species in use in breeding programs. Here we present de novo assemblies and annotations of eleven shrub willow genomes from six species. Copy number variation of candidate sex determination genes within each genome was characterized and revealed remarkable differences in putative master regulator gene duplication and deletion. We also analyzed copy number and expression of candidate genes involved in floral secondary metabolism and identified substantial variation across genotypes, which can be used for parental selection in breeding programs. Lastly, we report on a genotype that produces only female descendants and identified gene presence/absence variation in the mitochondrial genome that may be responsible for this unusual inheritance.