Format: ORAL

Radim J. Vaut1, Jana Geržov1, Veronika Ciesarkov1, Veronika Chodilov1, Lucie Kobrlov1, Zdenek pek1, Jan Weger2

1 Palacky University Olomouc, Olomouc, Czechia 2 Silva Tarouca Research Institute for Landscape and Ornamental Gardening, Pruhonice, Czechia

Weeping willow (Salix babylonica L.) and twisted willow (S. matsudana Koidz.) are prominent ornamental willows in temperate regions of the world. In addition, their importance has been growing in recent years due to their use as a promising crop for biomass production. Despite their distinctive morphologies, the taxonomy of this ornamental group, which also includes cultivars of presumed hybrid origin, has been characterised by uncertainty and confusion. Previous taxonomic concepts lacked exact (genetic) data and relied instead on morphological surveys. The considerable intraspecific phenotypic variation in willows and the lack of knowledge of the genetic relationships of taxa within S. babylonica/S. matsudana group have prevented experts from reaching a consensus on the number of accepted taxa of weeping and twisted willows. In our study, we used genome-wide genotyping using DArTseq (Diversity Arrays Technology) to analyse all major cultivars of S. babylonica/S. matsudana and their putative hybrids. By examining thousands of binary SNPs for each chromosome pair, complemented by data on genome size variation (estimated by flow cytometry), we gained new insights into the delimitation of taxa and cultivars within the S. babylonica/S. matsudana group. The results clearly show their close genetic relationship. We identified three major and four minor hybrid groups, and elucidated the origin of over 20 cultivars, including all the most widely grown cultivars. By providing a solid basis for understanding the genetic relationships between taxa within the S. babylonica group, and by providing compelling evidence for the origin of S. babylonica hybrids, we propose nomenclatural changes. These proposed changes aim to provide a stable taxonomic concept for this immensely popular, widely cultivated and aesthetically pleasing group of ornamental trees, potentially resolving uncertainties and errors that have persisted for nearly two centuries.