Investigation of the phylogenetic relationships within the genus Citrus (Rutaceae) and related species in Korea using plastid trnL- trnF sequences

Abstract

The phylogenetic relationships within the genus Citrus and related species found in Korea were analyzed by comparing the trnL- trnF intergenic spacer sequences of the chloroplast DNA (cpDNA). All 21 accessions had trnL- trnF sequences of identical length, 372 base pairs (bp). Of the 377 aligned positions in the trnL- trnF regions of these species, 67 sites were variable (17.8%, 67/377). Pairwise sequence divergences in the trnL- trnF region ranged from 0 to 3.2% in the ingroup accessions and from 8.8 to 10.9% between the in- and the outgroup species Phellodendron amurense. The greatest divergence (3.2%) was between C. aurantium and C. natsudaidai. A phylogenetic tree was generated based on maximum parsimony (MP) analysis of the trnL- trnF sequences data from 22 accessions, including the outgroup taxon, producing 17 equally most parsimonious trees. The consensus tree contained eight independent clusters. Cluster I contained C. platymamma, which has a collared fruit shape, unique among Korean Citrus. Cluster II contained mostly mandarin and pummelo accessions. Cluster V contained C. sunki and six accessions of C. unshiu. Four of six C. unshiu accessions had identical sequences. In addition, Nagami kumquat ( Fortunella margarita) was phylogenetically close to Citrus, whereas the trifoliate orange ( Poncirus trifoliate) was distant from Korean Citrus species, both local species and cultivars. These results confirmed that analyses of cpDNA trnL- trnF sequences can detect enough polymorphisms to differentiate Korean Citrus species and to determine their phylogenetic relationships.