Abstract
The genus Ditylenchus has been divided into 2 groups: the Ditylenchus triformis-group, and the Ditylenchus dipsaci-group based on morphological and biological characters. A total of 18 populations belong to 5 species of Ditylenchus was studied: Ditylenchus africanus, Ditylenchus destructor, Ditylenchus myceliophagus and dipsaci, Ditylenchus weischeri, the first 3 belong to the Ditylenchus triformis-group, the last 2 the Ditylenchus dipsaci-group. The species of Ditylenchus triformis-group were cultured on fungi, while the species from Ditylenchus dispaci-group cultured on excised roots of plant hosts in petri dish. DNA sequences of regions of the nuclear ribosomal first internal transcribed spacer (ITS1) and the small subunit 18S were PCR amplified, sequenced and the phylogenetic analyses also including the sequences of the closely related species from the GenBank. The randomly amplified polymorphisms of genomic DNA (RAPD) were also generated. Two clusters or clades corresponding to the 2 groups were consistently observed with significant statistical support from the 3 datasets. The phylogenetic analysis also revealed that the genus is paraphyletic, separating the 2 groups by species of Anguina and Subanguina.
Highlights
The genus Ditylenchus Filipjev (1936) consists of 80-90 accepted species (Brzeski 1991) of either mycophagous, entomophlic or plant parasitic species
DNA sequences: Ribosomal DNA fragments of the internal transcribed spacer 1 (404 bp) and fragments of the 18S ribosomal RNA gene (902 bp) were amplified and sequenced and sequences deposited in GenBank
Phylogeny: Phylogenetic trees based on the internal transcribed spacer 1 (ITS1) and 18S sequences of rDNA are shown in Figures 1 and 2 respectively
Summary
The genus Ditylenchus Filipjev (1936) consists of 80-90 accepted species (Brzeski 1991) of either mycophagous, entomophlic or plant parasitic species. The genus includes some of the most destructive nematode pests, e.g. the mushroom spawn nematode D. myceliophagus Goodey 1958, the potato rot nematode D. destructor Thorne 1945, and the stem and bulb nematode D. dipsaci (Kühn, 1857) Filipjev 1936, the latter two are internationally quarantined. Taxonomy of the genus both above and below the rank has been confusing. The genus was first placed in the family Tylenchidae of Tylenchina (Filipjev 1936), moved to Anguillulina Schneider (1939) and moved again to Anguinidae (Paramonov 1970). Recent phylogenetic studies of ribosomal DNA indicated that the genus may be paraphyletic (Holterman et al 2009; Giblin-Davis et al 2010)
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