Molecular phylogeny of the nematode genus Longidorus ( Nematoda: Longidoridae) with description of three new species.

The phylum Nematoda includes the genus Longidorus, a remarkable group of invertebrates that are polyphagous root-ectoparasites of many plants including various agricultural crops and trees. Damage is caused by direct feeding on root cells as well as by transmitting nepoviruses. Species discrimination in Longidorus is complicated by phenotypic plasticity (intraspecific variability and minor interspecific differences) leading to potential misidentification. We conducted nematode surveys in cultivated and natural environments in southern Spain that detected 11 species of Longidorus. We developed a comparative study amongst these related species by considering morphological and morphometric features together with molecular data from nuclear ribosomal RNA genes [ D2- D3 expansion segments of large ribosomal subunit (28 S), internal transcribed spacer 1 ( ITS1), and partial small ribosomal subunit ( 18S)]. The results of our molecular and phylogenetic analyses confirmed the morphological hypotheses and allowed the delimitation and discrimination of three new species of the genus, described herein as Longidorus baeticus sp. nov., Longidorus oleae sp. nov., and Longidorus andalusicus sp. nov., and eight known species ( Longidorus alvegus, Longidorus crataegi, Longidorus fasciatus, Longidorus intermedius, Longidorus iuglandis, Longidorus magnus, Longidorus rubi, and Longidorus vineacola). Phylogenetic analyses of Longidorus spp. based on the three molecular markers resulted in a general consensus of these species grouping, as lineages were maintained for the majority of species (i.e. species with a conoid-rounded lip region, amphidial fovea asymmetrically bilobed, female tail bluntly rounded), but not in some others (i.e. positions of L. crataegi, L. intermedius, and L. rubi were quite variable). To date, this is the most complete phylogenetic analysis for Longidorus and Paralongidorus species, with the highest number of species included. No correspondence between phylogenetic trees and morphological characters was found for ribosomal markers, with the exception of amphidial shape. Thus, polyphasic identification, based on integration of molecular analysis with morphology, is a tool beyond doubt in Longidorus identification. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]