Identification and relationship of old Japanese Hydrangea cultivars in Europe by morphological and nuclear SSR analysis

Hydrangea (hortensia) is an important ornamental plant as garden tree and as pot plant. Old Japanese cultivars have been introduced from Japan to Europe since the 18^th century. However, it has not yet been confirmed whether these old cultivars imported to Europe are identical with old cultivars existing in Japan. In this study, we did a morphological and molecular analysis of 20 Japanese old cultivars in Europe (Belgium, France and Italy) using nine sets of nuclear simple sequence repeats (SSR) markers for their identification and relationship. Six old cultivars were the same cultivars originated from Japan and Europe. However, other old cultivars did not show identical SSR profiles and some cultivars were classified in different clusters originating from Japan and Europe by structure analysis. For example, 'Benigaku', from Europe or from Japan was morphologically the same, however, SSR analysis exhibited the different genotype. SSR analysis also supports the record that 'Sekkayae' was a bud mutation of 'Nigra'. These results revealed the complex history of introduction and distribution of old Japanese cultivars into Europe since the 18^th century.