Originating in China over three millennia ago, Camellia sinensis, commonly known as tea, has undergone a significant transformation from its initial role as a medicinal herb to its current status as a globally favored beverage. While extensive investigations have been dedicated to tea plants in China’s southwestern regions, a notable lack of focus has been placed on those indigenous to Hainan Island. The striking morphological similarities between Hainan tea and Camellia sinensis var. assamica, coupled with the island’s distinctive environmental and climatic characteristics, have posed considerable obstacles to research endeavors concerning Hainan tea. A recent scientific undertaking endeavors to address this knowledge deficit by gathering 500 tea tree specimens from Hainan and conducting whole-genome resequencing to meticulously analyze genetic divergences between Hainan tea and established cultivated varieties of Camellia sinensis.
Guo et al. confirmed the distinct taxonomic position of Hainan tea within Camellia sinensis, providing valuable insights for resource conservation and molecular breeding. Image credit: Lin2015.
Tea represents China’s most ancient documented arboreal crop, with a history of domestication extending beyond 3,000 years.
Initially utilized as a botanical remedy, with its origins tracing back approximately 5,000 years, it subsequently transitioned into a widely adopted beverage for general consumption.
On a worldwide scale, cultivated tea varieties are broadly categorized into two principal lineages: Camellia sinensis var. sinensis and Camellia sinensis var. assamica.
Hainan Island, situated in the northern expanse of the South China Sea, possesses a rich heritage of tea plant cultivation and exhibits substantial areas dedicated to its growth.
Historical accounts from the latter part of the Qing Dynasty have attested to the prolific tea plant resources present on Hainan Island.
For instance, Benjamin Couch Henry, an American missionary and botanist, documented a significant proliferation of wild tea trees during his extensive expeditions within the Li ethnic group territories of Hainan, thereby substantiating the abundance of ancient tea tree genetic stock on the island.
Given that the Yunnan-Guizhou Plateau is widely considered a probable geographical cradle of tea, the majority of genomic studies focused on tea plant populations have incorporated specimens from southwestern China, with a particular emphasis on Camellia sinensis var. assamica cultivars. Consequently, scholarly attention directed towards the tea flora of Hainan Island has remained relatively limited.
“Our research serves to elucidate the taxonomic classification of Hainan tea and underscores its critical importance for both conservation initiatives and advancements in molecular breeding,” stated Dazhong Guo, a researcher affiliated with Yunnan Agricultural University, and his collaborators.
Within the scope of this investigation, the researchers meticulously sequenced the genomes of 500 tea tree samples, encompassing specimens from ancient tea trees, which were procured from four principal tea-producing districts on Hainan: Ledong, Qiongzhong, Baisha, and Wuzhishan.
A comprehensive dataset of 6.9 terabytes of raw sequencing data was generated. This data underwent rigorous filtering and was subsequently aligned against the reference genome (Yunkang 10), culminating in an average alignment rate of 98.98%.
Following the process of variant calling, an identification of 32,334,340 single nucleotide polymorphisms (SNPs) was achieved. The preponderance of these SNPs were located within intergenic regions, with a lesser proportion found within exonic segments.
Phylogenetic analyses employing SNP data revealed that the Hainan tea samples coalesce into a distinct cluster, setting them apart from the globally recognized Camellia sinensis var. sinensis and Camellia sinensis var. assamica groupings. While notable geographic aggregation was observed within the Limu Mountain region, a clear pattern was not discernible in other surveyed areas.
Further analyses of population structure corroborated that Hainan tea possesses a unique genetic makeup when contrasted with its global counterparts.
Principal component analysis (PCA) provided supporting evidence for these findings, demonstrating that Hainan tea is genetically differentiated from both Camellia sinensis var. sinensis and Camellia sinensis var. assamica, albeit exhibiting certain genetic affinities with the global Camellia sinensis var. assamica varieties.
Moreover, analyses of gene flow indicated restricted historical interbreeding between Hainan tea and other tea varietals, thereby reinforcing its distinct evolutionary trajectory.
Kinship assessments suggested that the close genetic relationships observed in specific Hainan tea samples were influenced by anthropogenic activities within managed tea plantations.
Investigations into genetic diversity uncovered elevated levels of diversity within populations from Hainan and the Limu Mountain region when compared to Camellia sinensis var. sinensis and Camellia sinensis var. assamica. Minimal genetic divergence was noted between Hainan tea and Limu Mountain tea.
These findings collectively underscore the unique evolutionary pathway pursued by Hainan tea, offering profound insights into its genetic heritage and carrying significant implications for strategies related to conservation and genetic improvement.
The distinct genetic profile and substantial diversity of Hainan tea position it as a potentially invaluable resource for forthcoming plant breeding initiatives.
“Our research contributes to a more profound comprehension of Camellia sinensis evolution and lays the groundwork for subsequent investigations into the genetic underpinnings of Hainan’s remarkable botanical resources,” the researchers commented.
Their publication appeared in the esteemed journal Agrobiodiversity.
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Dazhong Guo et al. 2024. Genome resequencing reveals an independently originated Camellia sinensis variety – Hainan tea. Agrobiodiversity 1 (1): 3-12; doi: 10.48130/abd-0024-0003
