Journal of Tea Science Research, 2024, Vol.14, No.4, 202-214 http://hortherbpublisher.com/index.php/jtsr 207 5 Case Study 5.1 Research on the collection and identification of tea germplasm resources The collection and identification of tea germplasm resources are crucial for conserving and utilizing the genetic diversity of tea plants. For instance, the Russian tea gene bank has collected representative tea germplasm resources from northern regions [Camellia sinensis (L.) O. Kuntze], including local varieties and radiation-induced mutants from the marginal germplasm banks located in Sochi and Maykop, Russia. These mutants often exhibit larger genome sizes and may have enhanced adaptability to biotic and abiotic stresses, providing potential genetic resources for tea cultivation in extreme environments. The study analyzed 43 mutants and clonally selected tea varieties using microsatellite (SSR) and start codon targeted (SCoT) markers, finding that SSR markers are more effective than SCoT markers in assessing the genetic diversity of polyploid tea germplasm resources. The results indicate that 106 genotypes in the Russian tea germplasm collection can be divided into three major genetic clusters. Despite the low genetic variation between clusters, the genotypes of tea cultivated in the northernmost regions show a greater genetic distance from those of the other two clusters, suggesting a unique genetic background. Additionally, the study revealed a significant moderate correlation between genome size and leaf area, providing important insights for the development of future tea germplasm conservation strategies and modern breeding programs (Samarina et al., 2022). Another study in Korea collected 410 tea tree accessions. The research indicates that 85.4% (350 accessions) of the 410 tea tree germplasms were collected from Jeollanam-do, revealing relatively low genetic diversity and a simple population structure in Korean tea germplasm resources (Lee et al., 2019). The analysis of molecular variance (AMOVA) showed that most of the genetic variation (99%) exists within populations rather than among populations (1%), indicating that the genetic differentiation is mainly concentrated within populations. This study provides a scientific basis for the effective collection, conservation, and utilization of tea germplasm resources. It also suggests that future tea breeding efforts should focus more on introducing and conserving diverse germplasm resources to enhance the genetic diversity and stress resistance of new varieties. Figure 2 Genetic structure of the 106 tea accessions assessed by 7 SSR markers. Red labels indicated the genotypes with increased genome size, comparing to control cv. 'Kolkhida' and cv. 'Sochi' (Adopted from Samarina et al., 2022) Image caption: The figure shows three clusters of 106 tea genotypes. The first cluster includes 31 cold-resistant genotypes grown in the northernmost regions, the second cluster mainly consists of hybrid varieties derived from Qimen germplasm and some mutants, while the third cluster comprises polyploid large-leaf mutants with increased genome size. The structural analysis indicates a high level of genetic admixture among different clusters, confirming the complex genetic background of these germplasm resources. Additionally, several genotypes in the third cluster exhibit typical Qimen characteristics, suggesting that they might be hybrids of Qimen varieties with other types (Adapted from Samarina et al., 2022)
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