Weak population differentiation and high diversity in Salsola tragus in the inland Pacific Northwest, USA

BACKGROUND: Salsola tragus is a widespread and problematic weed of semi-arid wheat production globally, and in the inland Pacific Northwest region of the USA. The species exhibits high levels of phenotypic diversity across its range and, at least in California USA, previous work has described cryptic diversity comprising a multi-species complex. Such cryptic diversity could suggest the potential for a differential response to management inputs between groups, and have important implications for the spread of herbicide resistance or other adaptive traits within populations. We used a genotyping-by-sequencing approach to characterize the population structure of S. tragus in the inland Pacific Northwest. RESULTS: Our results indicated that the population in this region is comprised of a single, tetraploid species (S. tragus sensu latu) with weak population structure on a regional scale. Isolation-by-distance appears to be the primary pattern of structure, but an independent set of weakly differentiated clusters of unknown origin were also apparent, along with a mixed mating system and high levels of largely unstructured genetic diversity. CONCLUSIONS: Despite considerable phenotypic variability within S. tragus in the region, agronomic weed managers can likely consider it as a single entity across the region, rather than a collection of cryptic subgroups with possible differential responses to management inputs or agroecosystem conditions. A lack of strong barriers to migration and gene flow mean that adaptive traits, such as herbicide resistance, can be expected to spread rapidly through populations across the region.