Nematology, 2010, Vol. 12(2), 171-180 Phylogenetic relationships, based on SSU rDNA sequences, among the didelphic genera of the family Trichodoridae from Portugal Isabel M. DUARTE 1,∗ , Maria Teresa M. DE ALMEIDA 2 , Derek J.F. BROWN 3 , Isabel MARQUES 4 , Roy NEILSON 5 and Wilfrida DECRAEMER 6 1 Departamento de Biologia e Ecologia, Escola Superior Agrária de Coimbra, Bencanta, 3040-316 Coimbra, Portugal 2 Departamento de Biologia, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal 3 Central Laboratory of General Ecology, Gagarin Street 2, 1113 Sofia, Bulgaria 4 Instituto Gulbenkian de Ciência, Rua da Quinta Grande, 6, 2781-901 Oeiras, Portugal 5 Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK 6 Royal Belgian Institute of Natural Sciences, Brussels, Belgium Received: 31 January 2009; revised: 15 May 2009 Accepted for publication: 18 May 2009 Summary – A survey of virus vector trichodorid nematodes was carried out in the central and northern regions of Portugal. Morphobio- metric identification showed the presence of trichodorid species previously reported from Portugal, except for Paratrichodorus porosus, which is reported for the first time in Continental Europe. Small subunit ribosomal DNA (SSU rDNA) sequences of ten different species occurring in Portugal were obtained and a phylogenetic analysis based on their alignment was performed to infer relationships among the different Portuguese trichodorid species and three non-indigenous populations (Nanidorus minor, P. allius and P. teres). The re- sulting phylogenetic tree is in agreement with the currently accepted classification for Trichodoridae, except for Nanidorus, which clusters together with Trichodorus species, while the genera Paratrichodorus and Trichodorus appear as two distinct groups. A better understanding of the generic groupings in the family Trichodoridae was found. Based on the new molecular analyses we herein accept Nanidorus as a valid genus. Keywords – 18S rDNA, molecular, Nanidorus, Paratrichodorus, Paratrichodorus porosus, phylogeny, tobacco rattle virus (TRV), Trichodorus, Tylolaimophorus minor. Of the 102 species that represent the five genera currently recognised by most authors in the Trichodoridae family, only a few didelphic species are known as virus vectors (Almeida & Decraemer, 2005; Decraemer & Robbins, 2007). The monodelphic genera, only recorded in Central and South America, have, as yet, no virus vector species. Trichodorid nematodes of the genera Paratrichodorus and Trichodorus are known as natural vectors of the three members of the Tobravirus genus, viz., Tobacco rattle virus (TRV), Pea early-browning virus (PEBV) and Pepper ringspot virus (PepRSV), to many agronomically important crops (Taylor & Brown, 1997). Up to now, 16 trichodorid species have been reported in Portugal (Almeida & Santos, 1997), including some vectors of TRV (Brown & Weischer, 1998; Duarte et al., ∗ Corresponding author, e-mail: iduarte@esac.pt 2002). Based on conventional taxonomy, the trichodorid group is relatively well defined, especially at genus level. However, Karanastasi et al. (2001) reported differences in the ultrastructure of the cuticle that were not completely genus specific. Based on their observations, three groups were established, two conforming to the extant taxonomy, representing Paratrichodorus and Trichodorus, and a third group comprising species of both genera. Furthermore, very little is known about the molecular phylogeny of these species (Boutsika et al., 2004a, b). The 18S subunit of the ribosomal DNA (18S rDNA) is the most frequently used DNA region to study molecular phylogenetic relationships among nematodes. It has both conserved and variable regions and allows alignment of unrelated taxa and design of universal primers that © Koninklijke Brill NV, Leiden, 2010 DOI:10.1163/156854109X461721 Also available online - www.brill.nl/nemy 171