An analytical toolkit for polyploid willow discrimination

Polyploid breeding is an important means for creating elite willow cultivars, and therefore provokes an active demand for discriminating the ploidy levels of natural willow stands. In this study, we established an analytical toolkit for polyploid willow identification by combining molecular markers and flow cytometry (FCM). A total of 10 single-copy fully informative SSRs were chosen for marker-aided selection based on a segregation test with a full-sib willow pedigree and a mutability test with a collection of natural willow stands. Aided by these molecular markers, we performed polyploid selection in two tree species and two shrub species of the genus Salix. The ploidy levels of the investigated samples were further examined using a flow cytometer. It was previously shown that results from marker-aided selection were consistent with those from FCM measurements. Based on ploidy level assessment in different willow species, it was found that tree willows were dominantly tetraploid, whereas shrub willows were most frequently diploid. With this analytical toolkit, polyploids can be rapidly screened from a large number of natural stands; thereafter, the exact ploidy levels of the polyploid candidates can be efficiently confirmed by FCM. This analytical toolkit will greatly enhance polyploid breeding programs for willows.