An integrative approach to the study of Xiphinema brevicolle Lordello and Da Costa 1961, supports its limited distribution worldwide (Nematoda: Longidoridae)

Abstract

Xiphinema americanum group has a cosmopolitan distribution, with several species having particular importance as virus-vectors of four economically important nepoviruses naturally occurring in the USA with IAI quarantine status for Europe. The morphological diagnosis of the species is problematic due to the limited diagnostic characters, overlapping morphometrics and incomplete taxonomic descriptions. An ongoing issue within the X. americanum group is the determination of species belonging to the X. brevicolle subgroup. By using a phylogenetic framework, molecular and morphometric data of the topotype population we demonstrate that certain of the published DNA sequences have been misidentified and belong to closely related species such as X. taylori, X. diffusum or unknown/unidentified species. Studying again the morphology and morphometrics of populations identified as X. brevicolle from the Czech Republic the identity, phylogenetic position and genetic variability of these populations have been clarified. These belong to a different species that is described herein as X. parataylori n. sp. Multi-gene phylogenies were reconstructed using nuclear ribosomal (18S rRNA gene, ITS1 and ITS2 regions, D2-D3 expansion segments of 28S rRNA gene) and mitochondrial DNA (partial cox1 and nad4) and the position of X. brevicolle (topotype population) to the most closely related species is shown. Morphology and species specific sequences were linked and the worldwide distribution discussed. The validity of X. brevicolle and the long-standing controversies about the taxonomic status of X. diffusum and X. taylori have been clarified. Xiphinema taylori and X. diffusum may represent complexes of cryptic species, however more comprehensive studies involving additional populations and materials from the type localities are needed to support this hypothesis.