Phylogenetic Relationships Among Lance Nematodes Species: Agricultural Pathogens In The United States

Lance nematodes (Hoplolaimus spp.) are important plant parasites that feed on the roots of several field crops, grasses and trees.  In the United States, three species cause significant yield losses in agriculture: H. columbus, H. galeatus and H. magnistylus. Despite the economic importance of lance nematodes, little is known about the phylogeography and origin of these species in the United States. For this reason, we studied the evolutionary relationships between H. columbus, H.magnistylus and H.galeatus collected from agricultural soils in different southeastern states.  To build the phylogenies, we used the species morphology, biology, and sequences of the small subunit of the ribosomal gene (18S). We also sequenced the internal transcribed spacer 1 (ITS1) of H. columbus individuals collected from soybean and cotton fields in South Carolina, where the species was first described. The phylogenetic tree based on the 18S gene shows that H.magnistylus and H.galeateus form a clade along with H.stephanus and other undescribed Hoplolaimus species, while H. columbus shows a close relationship with H. seinhorsti in a different clade. Sequence alignments of the 18S and ITS1 regions of H.columbus from South Carolina showed very low variation. We found no correlation with geographic origin or host in diversity observed.  The results of this project will help elucidate the ecological and population genetic processes which affect establishment of this pest.