Scleroderris canker of conifer is caused by Gremmeniella abietina var. abietina, which comprises several taxa, including races, varieties,
and biotypes. The European race of G. abietina var. abietina was introduced into North America early in the century, most likely on
asymptomatic infected pine seedlings, and is currently widespread in eastern North America. In order to detect latent infections and
differentiate the North American and European races of the fungus, we developed oligonucleotide primers to amplify by PCR
portions of the ITS of the ribosomal DNA of G. abietina var. abietina. The 417 bp amplified DNA fragment comprises two Msp I
restriction sites in the NA race but only one in the EU race. DNA extractions directly from infected asymptomatic needles, or from
single fruiting bodies, followed by PCR amplification and Msp I digestion allowed the detection and race identification of both races
of G. abietina var. abietina from seedlings and branches of Pinus resinosa and P. banksiana. A nested PCR assay was sensitive enough
to detect the equivalent of a single infected seedling in a bulk sample of 1000 healthy seedlings. Validation tests were conducted by
comparing PCR and isolation assays with 104 fascicles. All samples for which the fungus was isolated yielded a positive PCR assay
and there was no false negative, i.e. samples for which the fungus was isolated but not detected by PCR. Among the samples from
which the fungus was not isolated, most yielded a negative PCR assay (71%), but a proportion (29%) yielded positive PCR assays.
In several of those cases, aggressive contaminants had apparently overgrown the pathogen. The method described here can lead to
the detection and race identification of the NA and EU races of G. abietina var. abietina directly from infected tissues without the
need to culture the fungus and should find applications in nursery inspection and quarantine.