PHYLOGENETIC RELATIONSHIP AMONG THE SECTION STENOPHORA IN THE GENUS DIOSCOREA BASED ON THE ANALYSIS OF NUCLEOTIDE-SEQUENCE VARIATION IN THEPHOSPHOGLUCOSE ISOMERASE (PGI) LOCUS

To determine the phylogenetic relationship of six species (Dioscorea g racillima, D. nipponica, D. quinqueloba, D. septemloba, D. tenuipes, a nd D. tokoro) in the section of Stenophora in the genus of Dioscorea, nucleotide sequence variation in 1073 bp of coding region of the phosp hoglucose isomerase (Pgi) locus was analyzed. Estimates of nucleotide diversity (pi) for D. gracillima, D. quinqueloba, D. tenuipes, and D. tokoro were 0.0020, 0.0005, 0.0025, and 0.0013, respectively. Deviatio n from neutrality in the pattern of polymorphism in these four species was not detected by the Tajima's test. The difference in the pattern of amino acid substitutions between divergence and polymorphism was no t observed by McDonald and Kreitman test. The obtained phylogenetic tr ees indicated that D. tokoro and D. tenuipes belonged to a monophyleti c clade, while the other four species formed a separate monophyletic g roup. The branch lengths of phylogenetic tree varied among species. D. nipponica had a significantly faster substitution rate compared to D. gracillima, D. quinqueloba, and D. septemloba.