Assessment of the genetic connectivity between farmed and wild populations of Undaria pinnatifida (Phaeophyceae) in a representative traditional farming region of China by using newly developed microsatellite markers

Undaria pinnatifida is an important economic macroalga extensively farmed in East Asia. Wild individuals of U. pinnatifida, which can be easily discriminated due to their peculiar morphology, are usually observed to occur on the cultivation infrastructure adjacent to the farmed ones in the farming area. The genetic connectivity between the wild and farmed populations, however, remains unidentified. In this study, 30 informative microsatellite markers were developed and characterized through the next-generation sequencing technology. Ten of them were used to analyze the genetic structure of wild and farmed populations sampled from a representative Undaria farm in Lushun (latitude: 38A degrees 47' N) from 2015 to 2017, with two wild populations from Qingdao (36A degrees 03' N) and Gouqi Island (30A degrees 42' N) as controls. The dendrogram clearly separated farmed populations from wild ones by large genetic distance. The Bayesian model-based structure analysis grouped all the populations into five clusters. The wild individuals on the farm were found to contain relatively a large proportion of membership originated from farmed ones. In contrast, nearly no wild membership was detected in the farmed populations. These results imply asymmetric gene flow between farmed and wild populations and indicate that the pedigree of farmed cultivars has been well maintained through artificial control in the current seedling production system. Efforts should be made to popularize this system for the benefits of sustainable utilization of cultivars in Undaria farming.