Occurrence and ITS diversity of wood‐associatedBursaphelenchusnematodes in Scots pine forests in Switzerland

Abstract

The quarantine pathogenBursaphelenchus xylophilus(pine wood nematode,PWN) represents a serious threat forPinusspecies in Europe. To exclude its presence in Switzerland, in 2010 and 2011 a countrywide survey was conducted in 102Pinus sylvestrisstands, chosen according to whether they contained dying or dead trees or were located in areas at risk ofPWNintroduction. In total, 285 trees (1–5 per site) were sampled. Nematodes were extracted from wood chips using a standard procedure, and identified to species by internal transcribed spacer (ITS) sequencing.Bursaphelenchusspecies were present in 34% of the trees, but noB. xylophiluswas identified, i.e.PWNis still not present in Switzerland. The nematodes found belonged to seven different species, withB. vallesianusthe most frequent species, followed byB. sexdentati,B. mucronatus kolymensisandB. eggersi. Three other species (B. borealis,B. pinophilus,B. poligraphi) were each only present in one or two trees. Three groups of sequences could not be assigned to a species because of the lack of matching reference sequences. The species composition found in Switzerland suggests co‐existence of southern and central EuropeanBursaphelenchusspecies. Intraspecific ITS variability differed considerably among the four most common species.Bursaphelenchus eggersi,B. mucronatus kolymensisandB. sexdentatihad several variable sites in the ITS region, resulting in multiple ITS genotypes in each species. In contrast, all 99B. vallesianusisolates had an identical ITS region. This could indicate a founder effect, and possibly thatB. vallesianusis not native to the Alpine region.