Author
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Handoo, Zafar |
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PALOMARES-RIUS, JUAN - Spanish National Research Council |
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NAVARRETE, CAROLINA - Spanish National Research Council |
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LIEBANAS, GRACIA - University Of Jaen |
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SUBBOTIN, SERGEI - California Department Of Food And Agriculture |
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CASTILLO, PABLO - Spanish National Research Council |
Submitted to: Zoological Journal of the Linnean Society
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/12/2014 Publication Date: 9/26/2014 Publication URL: http://handle.nal.usda.gov/10113/60993 Citation: Handoo, Z.A., Palomares-Rius, J.E., Navarrete, C.C., Liebanas, G., Subbotin, S.A., Castillo, P. 2014. Integrative taxonomy of the stunt nematodes of the genera Bitylenchus and Tylenchorhynchus (Nematoda, Telotylenchidae) with description of two new species and a molecular phylogeny. Zoological Journal of the Linnean Society. 172:231-264. Interpretive Summary: Nematodes are microscopic worms that cause global crop loss exceeding $100 billion annually. Stunt nematodes are an important group that feeds on the roots of many kinds of plants worldwide. A major problem with determining the extent of crop loss due to stunt nematodes is that the nematodes present in many areas are unknown. In this study, an ARS scientist from Beltsville, Maryland, in collaboration with scientists from Spain and California, identified stunt and closely related nematodes obtained during surveys of agricultural and natural environments in the United States and Spain. Two new and seventeen valid species of these nematodes were discovered. In addition, methods involving anatomical features obtained with light microscopes and high-powered electron microscopes were integrated with DNA sequence methodology to provide valuable details that allow these species to be identified. The results are significant because the new species could have agricultural importance and because the refined methodology allows different species to be distinguished from each other more easily. Therefore, this research will be used by research scientists, action agencies, and extension agencies involved in nematode research and control. Technical Abstract: The genera Tylenchorhynchus Cobb, 1913 and Bitylenchus Filipjev, 1934 contain 104 and 29 valid species, respectively, of plant-parasitic nematodes collectively known as "stunt nematodes”. Stunt nematodes have a broad geographical distribution in several continents and some species damage agricultural crops, viz. alfalfa, corn, sorghum. Tylenchorhynchus spp. are characterized by phenotypic plasticity with overlapping morphology and morphometry leading to potential misidentification. Consequently, application of integrative taxonomic approaches provides a major approximation to species delimitation based on integration of different perspectives, e.g., morphology and DNA sequences. We conducted nematode surveys in cultivated and natural environments in Spain and the United States from which we identified seventeen valid species within the studied samples, which were characterized by using morphological and morphometrical features together with molecular data from nuclear ribosomal DNA genes [D2-D3 expansion segments of large ribosomal subunit 28S, internal transcribed spacer 1 (ITS1), and partial small ribosomal subunit (18S)]. The results of light and scanning electron microscopic observations and molecular and phylogenetic analysis confirmed the morphological hypotheses and allowed the delimitation and discrimination of two new species of the genera described herein as Bitylenchus hispaniensis sp. n. and Tylenchorhynchus mediterraneus sp. n., and seventeen known species of Dolichodoridae. Phylogenetic relationships of Tylenchorhynchus and other Dolichodoridae based on the three molecular ribosomal markers resulted in a general consensus of these species groupings. The monophyly of the genera Tylenchorhynchus and Bitylenchus was accepted for all three rRNA fragments by the Shimodaira-Hasegawa test based on tree topologies. This report provides the most complete phylogenetic analysis of Tylenchorhynchus and Bitylenchus species conducted so far. |