Survey on Bursaphelenchus species in Switzerland
In the Valais canton in Switzerland, an increasing decline of Scots pines (Pinus sylvestris) has been observed since the 1970s. This decline is probably caused by various biotic and abiotic factors such as fluoride pollution, water stress, high summer temperatures, the age structure of the forests (many old trees), bark beetles and pathogens. Studies were carried out to assess the possible involvement of Bursaphelenchus species in the pine decline observed in Valais. 217 declining pine trees were sampled from various locations in Valais from 2001 to 2004. Bursaphelenchus species were found in 40 trees and their presence was associated with blue stain fungi. The following 5 species were identified: Bursaphelenchus vallesianus, B. mucronatus, B. sexdentati, B. leoni and B. silvestris. The most frequently found species were B. vallesianus (found in 75% of the Bursaphelenchus-infested trees) and B. mucronatus (20%). B. xylophilus (EPPO A1 list) was not detected in Switzerland. It is noted that in total, 40% of the dying or recently dead trees were infested by Bursaphelenchus species which could indicate that nematodes may play a significant role in pine decline. It is considered that more research on pathogenicity and insect vectors is needed to clarify the role of these Bursaphelenchus species in pine decline in Switzerland.
Sources
Polomski J, Schönfeld U, Braasch H, Dobbertin M, Burgermeister W, Rigling D (2006) Occurrence of Bursaphelenchus species in declining Pinus sylvestris in a dry Alpine valley in Switzerland. Forest Pathology 36(2), 110-118.