Lack of genetic variation of Bursaphelencus xylophylus in Portugal revealed by RAPD-PCR analyses

Abstract

Random Amplified Polymorphic DNA (RAPD-PCR) technique was used in order to assess the level of genetic variability and genetic relationships among 24 Portuguese isolates of pinewood nematode, Bursaphelenchus xylophilus, representative of the fully affected area in Portugal. Two additional isolates of B. xylophilus, representing North America and East Asia were included, and B. mucronatus was used as out-group. Twenty-eight random primers generated a total of 640 DNA fragments. The Nei & Li similarity index revealed a high genetic similarity among the Portuguese isolates (above 90%). Hierarchical cluster analysis was performed to illustrate the relatedness among the isolates. No indication for separate groups among the Portuguese isolates was obtained, and the low level of genetic diversity strongly suggests that they were dispersed recently from a single introduction. The lack of apparent relationship between the genetic and the geographic matrices of the Portuguese isolates limits the use of this technique for following recent pathways of distribution. Genetic distance of the Portuguese isolates towards an isolate from China was much lower as compared to an isolate from the USA. This confirmed previous results suggesting an East Asian origin of the Portuguese B. xylophilus.