BRILL Nematology 16 (2014) 125-136 Nematology brill.conVnemy Both SSU rDNA and RNA polymerase II data recognise that root-knot nematodes arose from migratory Pratylenchidae, but probably not from one of the economically high-impact lesion nematodes Katarzyna RYBARCZYK-MYDLOWSKA ^'^, Hanny VAN MEGEN ', Sven VAN DEN ELSEN ^ Paul MOOYMAN ^ Gerrit KARSSEN^, Jaap BARKER ^ and Johannes HELDER ^'* ' Laboratory of Nematology, Department of Plant Sciences, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands ^Museum and Institute of Zoology PAS, Wilcza 64, 00-679 Warsaw, Poland Plant Protection Service, Wageningen Nematode Collection, P.O. Box 9102, 6700 HC Wageningen, The Netherlands Received: 24 April 2013; revised: 14 June 2013 Accepted for publication: 18 June 2013; available online: 28 August 2013 Summary - In 2000 Siddiqi formulated a hypothesis stating that root-knot nematodes (Meloidogyne spp.) constitute a branch arising from yet atiother important group of plant parasites, the tnigratory Pratylenchidae. This hypothesis was solely based on morphological characteristics. Ribosomal DNA (rDNA) sequence analysis supports this hypothesis in its broad sense, but the more precise question about the identity of a migratory Pratylenchidae representative being closest to the most basal Meloidogyne species could not be addressed due to a lack of backbone resolution (Holterman et al, 2009). Here we present an extended small subunit rDNA sequence analysis and a data set of partial RNA polymerase II sequences from Pratylenchidae and basal Meloidogynidae. Our data point at members of the genus Pratylenchus as being closest to the common ancestor of the root-knot nematodes, but it was not possible unequivocally to identify a candidate lesion nematode species. Pratylenciius is a species-rich genus (ca 70 valid species), and we suggest that the species closest to the most basal root-knot nematode should be sought outside of the group of relatively well-characterised, agronomicaUy relevant, species. Keywords - (a)sexual reproduction, evolution, Meloidogyne, Meloidogyne ichinohei, plant parasitism, Pratylenchus, RNA polymerase, rpbl, SSU ribosomal DNA. Within the phylum Nematoda, the order Tylenchida harbours the largest and agronomicaUy most important groups of plant parasites. However, plant parasitism is not the only trophic group in this speciose clade as the insect and mite-parasitic suborder Hexatylina is nested within. In terms of economic impact, three tylenchid groups are most relevant, viz., root-knot {Meloidogyne spp.), le- sion (Pratylenchus spp.) and cyst nematodes (Heterodera and Globodera spp.). Root-knot and cyst nematodes are sedentary endoparasites that induce the formation of a feeding site in the roots of their host plant, whereas lesion nematodes are migratory endoparasites that continuously enter and leave the plant root. Also, from an application- oriented point of view, it is relevant to pinpoint in more detail the evolutionary relationship between the three fam- ilies, Meloidogynidae, Pratylenchidae and Heteroderidae, in which these genera currently reside. On the basis of (nearly) full-length small subunit ri- bosomal DNA (SSU rDNA) sequences, a sister relation- ship was inferred between members of the Meloidogy- nidae and Pratylenchidae on the one hand, and Heteroderi- dae and Hoplolaimidae on the other (Holterman et ai, 2009). Despite the fact that more and more data point to a close evolutionary relationship between lesion and root- knot nematodes, we do not have a detailed picture yet, as most of the research efforts are dedicated to the more distal members of Meloidogyne such as M. incognita, M. hapla and M. chitwoodi. * Corresponding author, e-mail: Hans.Helder@wur.nl ® Koninklijke Brill NY, Leiden, 2014 DOl;10.l 163/15685411-00002750