Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 2, 2001
Publication Date: January 1, 2002
Citation: Carta, L.K., Skantar, A.M., Handoo, Z.A. 2002. Molecular, morphological and thermal characters of pratylenchus spp. and relatives using the d3 segment of the nuclear ls 28srrna gene. Nematropica 31: 193-207.
Interpretive Summary: Plant parasitic nematodes are microscopic worms that cause eight billion dollars of crop damage each year in the United States, and nematodes called lesion nematodes are among the most destructive. Molecular identifications of parasitic nematodes are valuable when there is a problem with insufficient material for microscopic diagnosis, such as with international plant interception samples. To develop new ways of molecularly identifying lesion nematodes, we have determined the sequence of a specific nematode gene fragment called the large subunit(LS)28S rRNA gene in Pratylenchus teres, a suspected pathogen of South African cotton, P. convallariae, an ornamental pathogen from Europe and the Pacific Northwest, and P. agilis, one of the five most serious lesion nematode pathogens of soybean. They are compared with the closest molecular sequences in the literature and evaluated for diagnostic and genetic relationships. P. teres is not as closely related molecularly to P. crenatus as morphology might suggest, but is closer to it than to P. convallariae. The results are significant because they will help to provide more accurate diagnoses of potential pests and may help to better predict possible host ranges useful for quarantine purposes. This information will be used by nematode diagnostic labs and action agencies in the future.
Gene sequences are provided of the D3 segment of the LS 28S rRNA gene in Pratylenchus teres, P. convallariae and P. agilis. They are compared with the closest comparable molecular sequences and evaluated for potential diagnosis and molecular phylogeny. Different outgroups in this study resulted in improved resolution of parsimonious phylogenetic trees, underscoring the importance of a dorsal or ventral esophageal overlap within taxa of the Pratylenchinae. Highest bootstrap support for the full sequence is seen for P. convallariae and P. penetrans (100%) followed by P. crenatus and P. vulnus (66 %). The molecular sequence indicates Pratylenchus teres is more closely related to P. crenatus than to morphometrically similar P. convallariae, but its closest molecular relatives among taxa with known sequences appear to be P. neglectus (=minyus) and Hirschmanniella belli. P. convallariae is strongly supported as a sister of P. penetrans. P. agilis has a closer molecular affinity to P. hexincisus (3/313 nucleotides) than to P. scribneri (9/313 nucleotides) which was originally diagnosed as its closest relative. Congruence of trees with thermal, vulval and lip characters are evaluated.