Molecular characterisation and origin of the Coffea arabica L. genome

Restriction fragment length polymorphism (RFLP) markers were used in combin ation with genomic in situ hybridisation (GISH) to investigate the origin o f the allotetraploid species Coffea arabica (2n = 44). By comparing the RFL P patterns of potential diploid progenitor species with those of C. arabica , the sources of the two sets of chromosomes, or genomes, combined in C. ar abica were identified. The genome organisation of C. arabica was confirmed by GISH using simultaneously labelled total genomic DNA from the two putati ve genome donor species as probes. These results clearly suggest that C. ar abica is an amphidiploid formed by hybridisation between C. eugenioides and C. canephora, or ecotypes related to these diploid species. Our results al so indicate low divergence between the two constituent genomes of C. arabic a and those of; its progenitor species, suggesting that the speciation of: C. arabica took place relatively recently. Precise localisation in Central Africa of the site of the speciation of C. arabica, based on the present di stribution of the coffee species, appears difficult, since the constitution and extent of tropical forest has varied considerably during the late Quat ernary period.