TAXONOMY AND PHYLOGENY OF THE GENUS CITRUS BASED ON THE NUCLEAR RIBOSOMAL DNA ITS REGION SEQUENCE

摘要

The genus Citrus (Aurantioideae, Rutaceae) is the sole source of the citrus fruits of commerce showing high economicvalues. In this study, the taxonomy and phylogeny of Citrus species is evaluated using sequence analysis of the ITS regionof nrDNA. This study is based on 26 plants materials belonging to 22 Citrus species having wild, domesticated, andcultivated species. Through DNA alignment of the ITS sequence, ITS1 and ITS2 regions showed relatively high variationsof sequence length and nucleotide among these Citrus species. According to previous six-tribe discrimination theory bySwingle and Reece, the grouping in our ITS phylogenetic tree reconstructed by ITS sequences was not related to tribediscrimination but species discrimination. However, the molecular analysis could provide more information on citrustaxonomy. Combined with ITS sequences of other subgenera in the “true citrus fruit tree” group, the ITS phylogenetic treeindicated subgenera Citrus was monophyletic and nearer to Fortunella, Poncirus, and Clymenia compared to Microcitrusand Eremocitrus. Abundant sequence variations of the ITS region shown in this study would help species identification andtribe differentiation of the genus Citrus.