Genetic Diversity of Arabusta Coffee (Coffea arabica L. x Coffea canephora Pierre) and their Parental Genotypes
Gimase, James Mwita
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Coffee ranks second after petroleum in international trade. In Kenya, it supports over 600,000 households, contributes up to12% of export revenue and employs 30% of the total workforce in Agriculture. Arabica (Coffea arabica L.) and Robusta (Coffea canephora Pierre) are the two species under commercial cultivation. Arabica coffee has low genetic diversity and susceptible to Coffee Berry Disease (CBD) and Coffee Leaf Rust (CLR) while Robusta Coffee has considerable diversity and tolerant to CBD and CLR. Interspecific hybrids between the two species have been utilized as sources of resistance to CBD and CLR. Induced tetraploid Robusta genotypes were introduced to Coffee Research Foundation (CRF), Kenya from Uganda and crossed with four varieties of Arabica as female parents to obtain interspecific F 1 hybrids (Arabusta) that are resistant to CBD and CLR. This study was carried out at CRF to characterize the genetic diversity of 12 interspecific F 1 Arabusta hybrids, 3 induced tetraploid Robusta, 4 Arabica varieties, Hibrido de Timor and a diploid Robusta using 13 SSR and 10 RAPD molecular markers. Bean biochemical components and beverage quality were also analyzed. RAPD and SSR PCR products were electrophoresed in 2.3% (w/v) agarose gel with 1x TBE buffer system and visualized in a UV light after staining with ethium bromide solution. The SSR and RAPD data were scored for presence (1) or absence (0) of bands, analyzed for polymorphic rate, subjected to cluster analysis using XLSTAT software and a dendrogram constructed using Un-weighted Pair Group Method with Arithmetic Averages. Coffee oils were extracted by Soxhlet method while caffeine, trigonelline, chlogenic acids (CGA) and sucrose were detected by high performance liquid chromatography system. Sensory analysis was carried by a panel of six judges as per the Specialty Coffee Association of America (SCAA). Biochemical and sensory data were subjected to Analysis of Variance using COSTAT software, means separated by Student- Newman - Keuls (SNK, p≤0.05) and Principle components analysis (PCA) plotted using XLSTAT software. SSR data revealed polymorphism of 51.5%, 50% and 6.9% for induced tetraploid Robusta, interspecific F1 Arabusta hybrids and Arabica genotypes respectively. RAPD data revealed polymorphism of 51.6%, 47.4% and 3.5% for induced tetraploid Robusta, interspecific F1 Arabusta hybrids and Arabica genotypes respectively. Cluster dendrogram separated the genotypes into various group revealing variations and indicating their relatedness. Biochemical data revealed significant (p≤0.05) differences among the genotypes for Caffeine, oils and sucrose but was not significantly different for CGA and trigonelline. Sensory data revealed highly significant (p≤0.05) differences for all the attributes. All the F1 hybrids scored above 80 points for total score, values that were similar to SL28 and SL34. This study revealed high genetic diversity and good cup quality for F 1 hybrids hence recommended for conservation, utilization in breeding programs, further study for adaptability and selection for release as coffee varieties.