The genus Salix, comprising some 400-500 species, is important in various alluvial or wet habitats of the northern hemisphere. It is a promising crop for applications such as biomass production, biofuels, or environmental projects. Clear species delimitation is crucial in ecology, biotechnology, and horticulture. DArTseq markers, a genome-wide technique, were tested for species and hybrid identification. A total of 179 willow samples were analysed, including six species of Salix subgen. Salix and four species of Salix subgen. Vetrix, including those used in biomass crop production, representing important European taxa. Identification of species-specific markers, clustering analyses (principal coordinate analysis, neighbor-joining) and Bayesian methods (Structure) unambiguously identified putative hybrids. In addition to demonstrating the high efficiency of DArT-seq markers in identifying willow hybrids, we also opened-up new questions about hybridisation processes and systematics. We detected unidirectional hybridisation between S. alba and S. fragilis, forming backcross hybrids, and we rejected the hypothesis that S. fragilis does not occur naturally in Europe. Further, the isolated position of Salix triandra within the genus was confirmed.

Department of Biology Faculty of Education Palacky University Olomouc 779 00 Olomouc Czech Republic

Department of Botany Faculty of Science Palacky University Olomouc 783 71 Olomouc Czech Republic

Department of Phytoenergy Silva Tarouca Research Institute for Landscape and Ornamental Gardening Public Research Institute 252 43 Průhonice Czech Republic

The Nature Conservation Agency of the Czech Republic Moravian Silesian Regional Branch 756 61 Rožnov pod Radhoštěm Czech Republic

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