Phylogenetic relationships within the cyst-forming nematodes (Nematoda, Heteroderidae) based on analysis of sequences from the ITS regions of ribosomal DNA

The ITS1, ITS2, and 5.8S gene sequences of nuclear ribosomal DNA from 40 ta xa of the family Heteroderidae (including the genera Afenestrata, Cactodera , Heterodera, Globodera, Punctodera, Meloidodera, Cryphodera, and Thecaverm iculatus) were sequenced and analyzed. The ITS regions displayed high level s of sequence divergence within Heteroderinae and compared to outgroup taxa . Unlike recent findings in root knot nematodes, ITS sequence polymorphism does not appear to complicate phylogenetic analysis of cyst nematodes. Phyl ogenetic analyses with maximum-parsimony, minimum-evolution, and maximum-li kelihood methods were performed with a range of computer alignments, includ ing elision and culled alignments. All multiple alignments and phylogenetic methods yielded similar basic structure for phylogenetic relationships of Heteroderidae. The cyst-forming nematodes are represented by six main clade s corresponding to morphological characters and host specialization, with c ertain clades assuming different positions depending on alignment procedure and/or method of phylogenetic inference. Hypotheses of monophyly of Puncto derinae and Heteroderinae are, respectively, strongly and moderately suppor ted by the ITS data across most alignments. Close relationships were reveal ed between the Avenae and the Sacchari groups and between the Humuli group and the species H. salixophila within Heteroderinae. The Goettingiana group occupies a basal position within this subfamily. The validity of the gener a Afenestrata and Bidera was tested and is discussed based on molecular dat a. We conclude that ITS sequence data are appropriate for studies of relati onships within the different species groups and less so for recovery of mor e ancient speciations within Heteroderidae. (C) 2001 Academic Press.