Description of Bursaphelenchus populi sp n. (Nematoda: Parasitaphelenchidae), a new member of the xylophilus group from aspen, Populus tremula L., in Europe

Bursaphelenchus populi sp. n. is described from dying and dead aspen trees, Populus tremula, in Poland. The nematode was found in trees infested with a long-horn beetle, Saperda perforata, and is vectored in the insect haemocoel. The characteristic morphology of male spicules, extended anterior vulval lip, lateral fields with four incisures, and number and arrangement of male caudal papillae, place B. populi sp. n. in the xylophilus group. Bursaphelenchus populi sp. n. can be separated from all other species in that group by the distinctive vulval flap, which is always bent with its distal half sunken in a conspicuous, sharp depression posterior to the vulva, and other morphological and morphometric characters, i.e., female tail shape, excretory pore position, spicule length (32.1 (25.7-37.0) mu m (as measured along arc) and shape, and a relatively long (i.e., L = 1020 (909-1111) mu m in females), and L = 850 (756-1055) mu m in males), and slender body (a = 45.4 (40.2-52.4) and 42.0 (36.1-49.3) in female and male, respectively). The status of the new species is confirmed by the unique molecular profile of the ITS region (ITS-RFLP). DNA sequencing and phylogenetic analysis of 28S rDNA region placed the new species close to B. fraudulentus in the xylophilus group. In vitro cross-breeding of the new nematode with B. xylophilus, B. mucronatus, B. fraudulentus and B. doui revealed full reproductive incompatibility between these species. In laboratory experiments on 2-year-old seedlings B. populi sp. n. was specific to aspen. It did not develop on pine or oak and reproduced only in weakened or dead aspen seedlings. No pathogenicity to the tree host or vector insect was observed. In Botrytis cinerea PDA cultures, body dimensions were significantly altered in both sexes and female tail morphology differed when compared to individuals extracted from aspen wood.