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Location: National Germplasm Resources Laboratory

Title: Characterization of Xiphinema americanum group species (Nematoda: Dorylaimida) and co-evolution of bacteria from the genus ‘Candidatus Xiphinematobacter’ with these nematodes

item Orlando, Valeria
item Chitambar, John
item Dong, Ke
item Chizov, Vladimir
item Mollov, Dimitre
item Bert, Wim
item Subbotin, Sergei

Submitted to: European Society of Nematologists
Publication Type: Abstract Only
Publication Acceptance Date: 6/15/2016
Publication Date: 8/28/2016
Citation: Orlando, V., Chitambar, J., Dong, K., Chizov, V., Mollov, D.S., Bert, W., Subbotin, S. 2016. Characterization of Xiphinema americanum group species (Nematoda: Dorylaimida) and co-evolution of bacteria from the genus ‘Candidatus Xiphinematobacter’ with these nematodes. European Society of Nematologists. Aug. 28.

Interpretive Summary:

Technical Abstract: The Xiphinema americanum group contains over two-dozen different species of nematode. They are economically important because they vector nepoviruses, which cause damage to several crops. Taxonomic differentiation among species of the X. americanum complex is problematic because many of the species share similar morphological characteristics and morphometric data, as well as a significant genomic overlap. We collected nematode samples from the X. americanum group in dispersed locations in the USA, Italy and Russia. These samples were examined for verrucomicrobial endosymbionts in addition to determining morphological data and genomic sequences of the nematode itself. Six valid species: X. americanum, X. californicum, X. brevicolle, X. pachtaicum, X. rivesi, X. simile and five unidentified putative Xiphinema species were characterized by morphology and by sequencing the D2-D3 segments of 28S rRNA and the mitochondrial (mt) COI genes. More than one hundred new sequences of nematodes and bacteria were generated. Phylogenetic relationships of the Xiphinema americanum group species were reconstructed using Bayesian inference. The analysis of the D2-D3 of 28S rRNA gene sequences did not provide clear species delimitation of the samples studied, however the mtDNA presented interspecific variations useful for demarcation among species. The species of X. americanum group harbor specific verrucomicrobial endosymbionts belonging to the genus ‘Candidatus Xiphinematobacter’. We provide evidence of several new Candidatus species based on 16S rRNA sequence analysis. Comparison of the bacteria (16S rRNA) and nematode (COI of mtDNA) phylogenies showed a high congruence in their topology, suggesting a high level of co-speciation between hosts and symbionts.