Phylogenetic studies on three <i>Helicotylenchus</i> species based on 28S rDNA and mtCOI sequence data

Abstract

To facilitate the process of spiral nematode species delineation, populations of <i>Helicotylenchus canadensis</i>, <i>H. pseudorobustus</i>, and <i>H. varicaudatus</i> deriving from various locations and diverse natural and anthropogenic environments from Poland were investigated and characterized. For the first time, 28S rDNA sequences are reported for <i>H. canadensis</i> and <i>H. varicaudatus</i>, whereas new mtCOI sequences were acquired for all three analyzed species. A Bayesian phylogenetic analysis of the 28S rDNA fragments revealed that <i>H. canadensis</i> and <i>H. varicaudatus</i> are members of a clade that is a sister group to all other <i>Helicotylenchus</i> species; however, the closest known sister group to <i>H. canadensis</i> is <i>H. vulgaris</i> type A. Both 28S rDNA- and mtCOI-based phylogenetic results suggest that this clade excludes <i>H. pseudorobustus</i>, whose most recent common ancestor with the former species was inferred to be the ancestor of all <i>Helicotylenchus</i> species. Moreover, within the mtCOI sequences obtained from <i>H. pseudorobustus</i>, unlike from the other two, a simultaneous presence of TAG and TAA codons was identified. This may indicate mitochondrial genetic code alterations or other genomic rearrangements in <i>H. pseudorobustus</i>.