Sequence-tagged sites (STS) for studies of molecular epidemiology of scleroderris canker of conifers

Scleroderris canker is a very damaging disease of conifers caused by a fungal pathogen, Gremmeniella abietina var 'abietina'. This fungal pathogen is now known to comprise a number of distinct races and biotypes. In North America, two races, an indigenous North American race and an introduced European race, are present. In Europe, three distinct biotypes have been reported within the European race: one in the Alps, another in Fennoscandia, and a third that overlaps with the first two. We used random amplified microsatellites (RAMS) and DNA sequencing with arbitrary primer pairs (SWAPP) to design five PCR primer pairs flanking polymorphic regions of the genome of the European race of G. abietina. Length polymorphisms produced by repeats of basic units in microsatellites were distinguished by electrophoresis of PCR products in agarose gels, and point mutations were identified by low-ionic-strength single-strand conformation polymorphisms (LIS-SSCP). Some primers generated private alleles in the European biotype and the psychrophilic Alpine and Fennoscandian biotypes, i.e., alleles that were fixed within the two groups but polymorphic between them. Conversely, one pair of primers amplified at least 3, 4, and 7 alleles in the Fennoscandian, Alpine, and European biotypes, respectively. The Alpine and Fennoscandian biotypes, although geographically separated, were genetically more closely related to one another than to European biotype, which has an overlapping distribution. However, both Alpine and Fennoscandian biotypes have similar ecotypic adaptation. The evolution of these biotypes could be explained by their geographic separation following the end of the last glaciation.