Insights into the Genetic Relationships and Breeding Patterns of the African Tea Germplasm Based on nSSR Markers and cpDNA Sequences - PubMed (original) (raw)

Insights into the Genetic Relationships and Breeding Patterns of the African Tea Germplasm Based on nSSR Markers and cpDNA Sequences

Moses C Wambulwa et al. Front Plant Sci. 2016.

Abstract

Africa is one of the key centers of global tea production. Understanding the genetic diversity and relationships of cultivars of African tea is important for future targeted breeding efforts for new crop cultivars, specialty tea processing, and to guide germplasm conservation efforts. Despite the economic importance of tea in Africa, no research work has been done so far on its genetic diversity at a continental scale. Twenty-three nSSRs and three plastid DNA regions were used to investigate the genetic diversity, relationships, and breeding patterns of tea accessions collected from eight countries of Africa. A total of 280 African tea accessions generated 297 alleles with a mean of 12.91 alleles per locus and a genetic diversity (H S) estimate of 0.652. A STRUCTURE analysis suggested two main genetic groups of African tea accessions which corresponded well with the two tea types Camellia sinensis var. sinensis and C. sinensis var. assamica, respectively, as well as an admixed "mosaic" group whose individuals were defined as hybrids of F2 and BC generation with a high proportion of C. sinensis var. assamica being maternal parents. Accessions known to be C. sinensis var. assamica further separated into two groups representing the two major tea breeding centers corresponding to southern Africa (Tea Research Foundation of Central Africa, TRFCA), and East Africa (Tea Research Foundation of Kenya, TRFK). Tea accessions were shared among countries. African tea has relatively lower genetic diversity. C. sinensis var. assamica is the main tea type under cultivation and contributes more in tea breeding improvements in Africa. International germplasm exchange and movement among countries within Africa was confirmed. The clustering into two main breeding centers, TRFCA, and TRFK, suggested that some traits of C. sinensis var. assamica and their associated genes possibly underwent selection during geographic differentiation or local breeding preferences. This study represents the first step toward effective utilization of differently inherited molecular markers for exploring the breeding status of African tea. The findings here will be important for planning the exploration, utilization, and conservation of tea germplasm for future breeding efforts in Africa.

Keywords: African tea germplasm; Camellia sinensis; breeding improvement; cpDNA regions; genetic diversity; nSSR markers.

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Figures

Figure 1

Figure 1

Bayesian assignment of probabilities using STRUCTURE based on 23 nSSR loci of the 280 tea accessions.

Figure 2

Figure 2

Geographical distribution of nSSR genetic groups considered following STRUCTURE analysis at K = 3. Each country is depicted as a pie chart with the proportional membership of its alleles to each one of the three groups. A shape file with genotype proportions in the different countries was generated in DIVA-GIS v7.5.0.0 (

http://www.diva-gis.org/

). The shape file was then used to generate the map in ArcGIS v10.2.2 (

http://www.esri.com/

).

Figure 3

Figure 3

Bayesian assignment of probabilities in NewHybrids for 280 tea accessions from Africa. The defined categories are parent 1 (P1), parent 2 (P2), first filial generation (F1), second filial generation (F2), backcross to P1 (BC1), and backcross to P2 (BC2).

Figure 4

Figure 4

Geographical distribution of the nine cpDNA found in the 280 samples across eight countries in Africa. The map was generated using DIVA-GIS and ArcGIS software as described in Figure 2.

Figure 5

Figure 5

Median-joining haplotype network based on three combined cpDNA regions of 84 tea samples from eight African countries. Broken lines delineate closely related haplotypes. Circles in colors denote different haplotypes (H1-H9), and the size of each circle is proportional to the number of accessions sharing that particular haplotype. Each branch between haplotypes denotes a mutational step. The small black circles represent independent mutation events converging on a shared haplotype.

Figure 6

Figure 6

Neighbor joining tree of 84 tea samples. Each color represents a particular haplotype and corresponds to colors in Figure 5.

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