![]() leviterminalis ( Chen et al., 2006), but comparable sequences from other relatives are lacking. ITS rDNA sequences are available in GenBank for T. Tied to morphology, similarity searches of sequences are especially useful when competing generic and subfamily names are used in the literature, as is currently the case for Telotylenchidae.Īn isolate of Tylenchorhynchus leviterminalis ( Siddiqi, Mukherjee and Dasgupta, 1982) Siddiqi, 1986 was identified by us from a foreign plant interception, and there are no records of this species’ existence in North America. ![]() Molecular sequences also provide important information on genetic variation of populations within morpho-species, and evaluating whether similar species that lack males should be synonymized with species that have them. These phylogenies can provide an independent means to understand character distribution that impacts stability of higher taxonomic categories. Molecular phylogenetic analyses are needed to evaluate competing taxonomic schemes and the characters on which they are based before any new names can be readily accepted. ![]() However, some of the newer generic names of stunt nematodes and relatives have been ignored in recent compendia for ease of practical identification ( Fortuner and Luc, 1987 Brzeski and Dolinski, 1998 Handoo, 2000), and the morphological characters to distinguish them are often not discrete. These taxa were based on different hierarchies of characters such as pharyngeal gland overlap, number of lines in the lateral field, male genitalia, and major differences in female terminal tail features ( Jairajpuri and Hunt, 1984 Gomez-Barcina et al., 1992). Since an earlier comprehensive review of Tylenchorhynchus sensu lato ( Allen, 1955), various taxonomic designations for stunt nematode genera have been proposed, from Merlinius, Quinisulcius and Uliginotylenchus listed in the compendium of Tarjan, 1973 through a current assemblage of five genera within Merliniinae Siddiqi, 1971, twelve genera in Telotylenchinae Siddiqi, 1960, and six junior synonyms under Tylenchorhynchus itself ( Siddiqi, 2000). Because of the large number of stunt nematode species, taxonomists have been motivated to simplify identification into more manageable generic units, but an unusual number of confusing and competing systems based on different character priorities now exist. Stunt nematodes ( Tylenchorhynchus sensu lato) and relatives within the Telotylenchidae Siddiqi, 1960 are extremely common in the rhizosphere of native and cultivated plants. Two putative species of Neodolichorhynchus failed to group together, and two populations of Scutylenchus quadrifer demonstrated as much or greater genetic distance between them than among three related species of Merlinius. robustus did not cluster with three Tylenchorhynchus spp. Contrary to some expectations from current taxonomy, Telotylenchus and Tylenchorhynchus cf. Conflicting generic and family nomenclature based on characters such as pharyngeal overlap are discussed in light of current molecular phylogeny. ![]() Extremely thickened tail termini arose at least once in Amplimerlinius and Pratylenchoides among ten species of Merliniinae plus three Pratylenchoides, and three times within twelve taxa of Telotylenchinae and Trophurinae. ![]() Thick-tailed Trophurus, Macrotrophurus and putative Paratrophurus did not group together in the 18S tree. Terminal tail thickness within Merliniinae, Telotylenchinae and related taxa showed a mosaic distribution. leviterminalis branched outside relatively narrow-tailed T. In 18S trees, similar terminal tail thickness was found in a well-supported clade of three Tylenchorhynchus: broad-tailed T. Tail shapes and hyaline termini were characterized for taxa within these subfamily trees, and variability discussed for some related species. Based upon comparably sized phylogenetic breadth of outgroups and ingroups, the 28S rDNA contained three times the number of phylogenetically informative alignment characters relative to the alignment total compared to the larger 18S dataset even though there were fewer than half the number of taxa represented. claytoni were characterized with segments of small subunit 18S and large subunit 28S rDNA sequence and placed in molecular phylogenetic context with other polyphyletic taxa of Telotylenchidae. Three stunt nematode species, Tylenchorhynchus leviterminalis, T. ![]()
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