Effectively using genomic information greatly accelerates conventional breeding and applying it to long-lived crops promotes the conversion to genomic breeding. Because tea plants are bred using conventional methods, we evaluated the potential of genomic predictions (GPs) and genome-wide association studies (GWASs) for the genetic breeding of tea quality-related metabolites using genome-wide single nucleotide polymorphisms (SNPs) detected from restriction site-associated DNA sequencing of 150 tea accessions. The present GP, based on genome-wide SNPs, and six models produced moderate prediction accuracy values (r) for the levels of most catechins, represented by ( −)-epigallocatechin gallate (r = 0.32–0.41) and caffeine (r = 0.44–0.51), but low r values for free amino acids and chlorophylls. Integrated analysis of GWAS and GP detected potential candidate genes for each metabolite using 80–160 top-ranked SNPs that resulted in the maximum cumulative prediction value. Applying GPs and GWASs to tea accession traits will contribute to genomics-assisted 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.

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Several metabolites define tea quality in new tea shoots composed of leaf and stem. To improve tea quality for breeding, it is important to understand the tissue-dependent genetic mechanisms and metabolic network responsible for the profile of tea quality-related metabolites. We analyzed the volatiles and specialized metabolites as the tea quality-related metabolites in leaves and stems of new shoots in 30 tea accessions to understand the tissue variation and network between tea quality-related metabolites. Our results provided the tissue-dependent variation network in the tea quality-related metabolites, including volatiles in new leaves and stems in tea accessions. Each volatile content in tea accessions showed the coefficient of variation ranging from 58.7 to 221.9% and 54.2 to 318.3% in new leaves and new stems, respectively. The accumulation pattern of tea quality-related metabolites in new leaves and stems varied depending on the accession. When comparing tea genetic populations, the profile of tea quality-related metabolites of new leaves, but not new stems, was the key to distinguishing tea genetic populations by chemical indicators. We described the network between tea quality-related metabolites, especially the dense network in new leaves. These results also will provide the key information for metabolic engineering and the selection of breeding materials in tea plants based on the tea quality-related metabolites and aid in understanding their molecular mechanisms and network of metabolic variation.

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