Performance of Interspecific Arabusta Coffee Hybrids for Yield, Cup Quality, and Disease Resistance.

Abstract

The Kenya annual coffee production has in recent years declined due to different factors such as change of land use and biotic stresses, despite the country being one of the world’s producers of high-quality coffee. This study analysed the agronomic potential of Arabusta hybrids developed from C. arabica and C. canephora for their bean yield, quality, and disease resistance. Nineteen Arabusta genotypes were assessed in two different locations (Siaya ATC and KALRO-Alupe) for growth and bean yield during the second and third years after establishment in the year 2017 and 2018 respectively. The data collected and analysed included plant height, number of bearing primaries, percentage of berries per node, length of longest primary, the total number of berries on the primary, berries per node, laterals, nodes with the highest number of berries, berries per node and yield (g/tree). Genetic variability among the genotypes was determined using 19 SSR markers. Marker Assisted Selection (MAS) using SSR marker SAT 235 was used to identify genotypes with the Ck-1 gene that are CBD resistant. The polymorphism between the Arabusta genotypes and the Arabica coffee varied, with 72% polymorphism calculated among Arabusta genotypes and 46.8% among the Arabica genotypes. The SSR marker SAT 235 was able to identify genotypes that have the CK-1 gene for coffee berry disease resistance. Genotypes and locations revealed differences that were significant for both growth and yield traits. There was a positive significant correlation between yield and percentage berries per node (r= 0.61), total number of berries on longest primary (r= 0.58), and total number of berries on each node on the longest primary(r=0.60). Arabusta hybrids that had higher yields when compared to other genotypes in Busia were ARH1, ARH4, and ARH5 whereas in Siaya it was ARH4. Significant variation in sensory and bean grade traits showed that Arabusta hybrids gave higher xx scores than backcrosses and Robusta. Acidity showed significant positive correlation with (r=0.96), aroma (r=0.84), balance (r=0.85), flavour (r=0.96) and preference (r=0.96). The 100 berry weight showed a positive correlation with the AA bean size indicating that berry weight can be used to predict AA bean size. Genotypes differed significantly in biochemical compounds across the two different environments. The environmental effects were significant for all the biochemical compounds except for chlorogenic acids, but the G x E effects were not significant. The correlation between the chlorogenic acids and caffeine was significantly positive (r=0.77) but its correlation with lipid oil was significantly negative (r=-0.49) and also with sucrose (r=-0.43). Arabusta hybrids scored over 80 % for the total score in cup quality comparing well with the Arabica coffee and outperforming the Robusta coffee (79.4%) thus qualifying for the specialty market. Arabusta hybrids, backcrosses, and Arabica coffee on average had higher levels of sucrose, oil, and trigonelline when compared to Robusta which was responsible for the improved liquor quality. This study confirmed that it is possible to transfer genes for high cup quality to Robusta from Arabica coffee through interspecific hybridization. The quantitative traits exhibited a highly significant positive correlation implying that these traits can be utilized in ensuring effectiveness and the efficiency of early selection for yield. The wider genetic variability of the Arabusta hybrids than that of Arabica coffee is key for coffee improvement programmes. All the hybrids and backcrosses did have the CK-1 gene responsible for CBD resistance. The Arabusta hybrids and the backcrosses had a score of > 80% on cup quality and therefore taking into consideration their performance in yield, the high yielding Arabusta hybrids ARH1, ARH4, and ARH5 are recommended for commercial cultivation in the specific environments.