Identification and evaluation of Forsythia germplasm using molecular markers

This study identifies Forsythia germplasm and evaluated the genetic relationships of F. ×intermedia hybrids, cultivars and their putative parental species. Leaf samples of F. ×intermedia cultivars and species, such as F. koreana and F. suspensa, were collected in the Netherlands, Korea, and USA. Total genomic DNA was extracted and evaluated by randomly amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analyses. Dendrograms were constructed by using the neighbor-joining (NJ) clustering algorithm applying the interior branch (IB) test or analyzed by STRUCTURE. In the dendrogram generated by RAPD markers, two major clusters were observed. One cluster (CL-I) contained most of the F. ×intermedia cultivars, F. suspensa, and F. koreana. The other cluster (CL-II) included F. europaea, F. ovata, F. densiflora, F. mandshurica, F. japonica, F. viridissima, and cultivars derived from F. ovata. In the AFLP dendrogram, the placement of F. ×intermedia cultivars with F. suspensa was similar, forming cluster CL-A I. The RAPD and AFLP results clearly separated most F. ×intermedia cultivars from F. ovata derived cultivars. The full range of genetic diversity of F. suspensa and F. viridissima should be investigated to verify whether these two species are truly parental taxa for F. ×intermedia. Placement of F. viridissima, F. ovata, and F. japonica in different sub-clusters requires further investigation regarding genetic diversity in the species, and their close relationship with F. koreana, F. mandshurica, and F. saxatalis.