Wood-Inhabiting Nematode, Bursaphelenchus ussuriensis sp. n. (Nematoda: Aphelenchoididae) from David Elm, with Molecular Phylogeny of the Genus Based on Partial Mitochondrial Genomes

A new nematode species, <i>Bursaphelenchus ussuriensis</i> sp. n. is described in the bark beetle-elm tree association (<i>Scolytus jacobsoni</i> and <i>Ulmus davidiana</i> var. <i>japonica f. suberosa</i>) in the Asian Pacific region of Russia. The new species belongs to the <i>Hofmanni</i> group of <i>Bursaphelenchus</i> and is closest to <i>B. ulmophilus</i>. Its characteristics are as follows: lateral field with three incisures, body length 497-771 µm, post-uterine sac 3.6-5.4 times vulval body diam, 56 (39-66)% of vulva-anus distance, and spicule length 10.3 (9.5-12.5 µm). The new species differs from all species of the <i>Hofmanni</i> group in the closely situated P3 and P4 male caudal papillae and the GP5 small 'glandpapillae' pair on the butterfly-like papillae plate, in the set of P1, P2, P3, P4, GP5; vs. in all other species, the P4 papillae pair is absent in the pattern of P1, P2, P3, GP5. The phylogenetic position of <i>B. ussuriensis</i> sp. n. with other species of the <i>Hofmanni</i> group were reconstructed using the D2-D3 expansion segments of 28S and ITS rRNA gene sequence analysis. Sequences of twelve mitochondrial protein-coding genes of <i>B. cocophilus, B. fraudulentus, B. michalskii, B. ussurensis</i> sp. n., and <i>B. willibaldi</i> were obtained in this study. Phylogenetic relationships among eighteen <i>Bursaphelenchus</i> species based on the analysis of the mtDNA sequence dataset are provided and discussed. A modified diagnosis of the <i>Hofmanni</i> group is proposed.