Origin, Evolution, and Diversity of the Coffee (Coffea arabica L.) Genome

The recent development of DNA-based techniques has broadened the horizon for investigating the composition and organization of the coffee genome. It was found to be small according to both nuclear DNA content data and estimates of physical and genetic size. The origin of the allotetraploid (2n = 4x = 44) species Coffea arabica was confirmed and the diploid (2n = 2x = 22) progenitors of the species were identified. High affinity was noted between the two subgenomes of C. arabica and between C. arabica and the diploid species, suggesting that speciation of C. arabica was a relatively recent event. Coffee cultivation, begun about 1,500 years ago in Ethiopia, has been characterized by successive reductions in genetic diversity within the wild gene pool. The transfer of genes from diploid coffee, in particular resistance genes, was also studied. There seemed to be a substantial extent of alien DNA in introgressed lines after several selfed generations. Disomic inheritance of molecular markers was found in the C. arabica genome while tetraploid interspecific hybrids of crosses between C. arabica and a duplicated diploid coffee presented tetrasomic inheritance. The results could be used to enhance breeding strategies based on gene introgression without lowering cup quality.