Analyses of single nucleotide polymorphisms identified by ddRAD-seq reveal genetic structure of tea germplasm and Japanese landraces for tea breeding

To obtain genetic information about the germplasm of tea (Camellia sinensis L.) in Japan, 167 accessions including 138 var. sinensis (96 Japanese var. sinensis and 42 exotic var. sinensis) and 29 Assam hybrids were analyzed using single nucleotide polymorphisms (SNPs) markers identified by double-digest restriction-site-associated DNA sequencing (ddRAD-seq) analysis. Approximately 10,000 SNPs were identified by ddRAD-seq and were mapped across the whole genome. The 167 tea accessions were classified into three genetic subgroups: (1) Japanese var. sinensis; (2) Japanese and exotic var. sinensis; (3) Assam hybrids and exotic var. sinensis. Leaf morphology varied widely within each genetic subgroups. The 96 Japanese var. sinensis were classified into four genetic subgroups as follows; two subgroups of Shizuoka (the largest tea production region) landraces, Uji (most ancient tea production region) landraces, and the pedigree of ‘Yabukita’, the leading green tea cultivar in Japan. These results indicated that the SNP markers obtained from ddRAD-seq are a useful tool to investigate the geographical background and breeding history of Japanese tea. This genetic information revealed the ancestral admixture situation of the ‘Yabukita’ pedigree, and showed that the genome structure of ‘Yabukita’ is clearly different from those of other Japanese accessions.