Weigela species and cultivar genome size and ploidy estimations: shrub breeding^©

INTRODUCTION
Weigela are among the most popular flowering shrubs for temperate landscapes as they tolerate a wide range of cultural conditions, propagate easily from cuttings, and flower heavily in late spring. The genus is composed of 10 species native to China, Japan, Manchuria, and the Korean peninsula. Since the genus was brought to western horticulture near 1860, over two hundred cultivars have been introduced (Dirr, 2009; Sheffield Botanical Gardens, 2015). Introductions continue today with breeding work emphasizing the development of compact plants, novel foliage colors, and recurrent blooming characteristics. One cultivar, ‘Courtalor’, Carnaval® weigela is widely promoted as a reblooming polyploid (Pantin, 2015; Wood). Because polyploidy may be associated with ornamental characteristics that breeders may be selecting for, such as reblooming, we set out to investigate the presence of polyploidy in natural populations and extent of polyploidy in available cultivars. This manuscript reports genome size and ploidy estimations for 10 species and 46 cultivars, from a total of 74 accessions.