Pine wilt is the most serious disease of native pines in Japan and potentially the most important nematode disease of conifers in the world. The pinewood nematode Bursaphelenchus xylophilus was found to be the causal agent. Difficulties arose with respect to the precise identity of some isolates of B. xylophilus and of similar species B. mucronatus and B. fraudulentus. Restriction enzyme analyses of repetitive DNA revealed bands specific for the species B. xylophilus, B. mucronatus and B. fraudulentus. Hybridization patterns obtained with unc-22 gene of C. elegans, clearly identified B. xylophilus, B. mucronatus and B. fraudulentus as well as the different geographic isolates of these species. Furthermore, it is possible to define the phylogenetic relationships between the different populations constituting the ‘pine wood nematode’ complex.

In and around the British Isles, three biologically specialized strains of the fish acanthocephalan Pomphorhynchus laevis have been recognized, each differing in geographical distribution and both final and intermediate host utilization. Six restriction endonuclease digests of the genomic DNA of the English freshwater and marine strains were compared by genomic cross-hybridization using the randomly sheared and radio-isotope labelled genomic DNA of freshwater P. laevis, and also by using a heterologous isotope labelled ribosomal DNA probe. Autoradiographs of hybridized Southern blots provided evidence for considerable homogeneity in the total repetitive DNA of the two strains as well as some preliminary evidence for possible restriction fragment length polymorphisms using EcoR I and Pvu II.