PHYLOGENETIC-RELATIONSHIPS OF COFFEE-TREE SPECIES (COFFEA L) AS INFERRED FROM ITS SEQUENCES OF NUCLEAR RIBOSOMAL DNA

Phylogenetic relationships of Coffea species were estimated from the s equences of the internal transcribed spacer (ITS 2) region of nuclear ribosomal DNA. The ITS 2 region of 37 accessions belonging to 26 Coffe a taxa and to three Psilanthus species was directly sequenced from pol ymerase chain reaction (PCR)-amplified DNA fragments. The level of var iation was high enough to make the ITS 2 a useful tool for phylogeneti c reconstruction. However, an unusual level of intraspecific variation was observed leading to some difficulty in interpreting rDNA sequence divergences. Sequences were analysed using Wagner parsimony as well a s the neighbour-joining distance method. Coffea taxa were divided into several major groups which present a strong geographical corresponden ce (i.e. Madagascar, East Africa? Central Africa and West Africa). Thi s organisation is well supported by cytogenetic evidence. On the other hand, the results were in contradiction with the present classificati on of coffee-tree taxa into two genera, namely Coffea and Psilanthus. Furthermore, additivity of parental rDNA types was not observed in the allotetraploid species C. arabica.