ITS-RFLP pattern of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) does not reflect nematode virulence

Abstract

Analysis of the restriction fragment length polymorphism of the internal transcribed spacer region of ribosomal DNA (ITS-RFLP) is an efficient tool for classifying Bursaphelenchus nematodes at or below the species level. In B. xylophilus, it has been shown that the ITS-RFLP pattern of Japanese avirulent (nonpathogenic) isolates is different from that of Japanese virulent (pathogenic) isolates. To clarify the relationship between the virulence and the ITS-RFLP pattern of B. xylophilus, an experiment involving inoculation of the nematodes was performed. Two types of nematode subculture that showed the same RFLP pattern as the virulent isolate or the avirulent isolate were produced from a new nematode population obtained in the field and inoculated into healthy pine seedlings. All seedlings inoculated with the nematode subcultures died within six months, irrespective of whether the subculture had the virulent or avirulent RFLP pattern; this indicated that the nematode virulence does not correspond with the ITS-RFLP pattern. This study shows that the ITS-RFLP pattern is not always available to discriminate between avirulent and virulent populations of B. xylophilus.