Intraspecific variations and phylogenetic relationships of steinernematids isolated from Japan based on the sequences of the ITS region of the nuclear rRNA gene and the partial mitochondrial COI gene

DNA sequences of the internal transcribed spacer (ITS) region of the nuclear rRNA gene and mitochondrial cytochrome oxidase I (COI) gene were used to analyze intraspecific variations and infer phylogenetic relationships of steinernematids isolated from Japan. DNA fragment lengths of the amplified ITS region obtained from 19 Japanese steinernematid isolates ranged from 914-1,067 bp and varied considerably among the species. A few intraspecific variations were detected in Steinernema litorale, Steinernema spp. MY6 and MY8, and no variation was observed in S. monticolum and Steinernema sp. MY5 in the sequences of the ITS region. The fragment length of the amplified partial COI gene was 397 bp for all species. The intraspecific variations of the sequences ranged from 0.3%-7.8% (0-42 nucleotide differences) for S. monticolum, S. litorale, Steinernema spp. MY5, MY6, and MY8. Sequence comparisons and phylogenetic analyses reveal that the sequence of the COI region can distinguish the isolates within a species but is not as effective as the ITS region in elucidating the relationship among species.