Molecular Evidence of Distinct Introductions of the European Race of Gremmeniella abietina into North America

Abstract

The presence of the European (EU) race of Gremmeniella abietina var. abietina, the causal agent of Scleroderris canker of conifers, was first reported in North America in 1975 in the northeastern United States and subsequently in southern Quebec and Newfoundland during the late 1970s, where it quickly became established. We analyzed DNA profiles in samples from a historic collection of G. abietina var. abietina that included some of the first isolates of the EU race reported in the United States to test hypotheses concerning the G. abietina var. abietina epidemic in North America. Genetic diversity was partitioned by an analysis of molecular variance with haplotype frequencies and distances. Genetic differentiation was high between populations in continental North America and Newfoundland (between region differentiation, Phi(ct) = 0.665, P < 0.001). This result was not consistent with the hypothesis of a single introduction of the pathogen into the northeastern United States followed by secondary spread into northeastern Canada. In contrast, small levels of genetic differentiation were observed among continental North American populations (Phi(ct) = 0.047, P = 0.079), suggesting gene flow among these populations. A single haplotype of G. abietina var. abietina dominated the continental populations (80% of the isolates) but was absent from Newfoundland and Europe. Five haplotypes were found in the New-foundland population, all of which were either absent or very rare on the continent. Populations from continental North America clustered together and were distinct from a second cluster composed of European and Newfoundland populations. A phylogenetic analysis of the haplotypes indicated that some of the rare haplotypes may have derived from somatic mutations, whereas others probably occurred as the result of new introductions. The results are consistent with a scenario of distinct primary introductions of this pathogen into Newfoundland and continental eastern North America followed by secondary asexual propagation.

Molecular epidemiology of forest pathogens: from genes to landscape

“…A single multilocus haplotype of G. abietina var. abietina dominated the continental populations but was absent from Newfoundland and Europe (Hamelin et al 1998a). Five haplotypes were found in Newfoundland, all of which were either absent or very rare in continental North American populations.…”

“…This contrasts sharply with the clonal nature of G. abietina var. abietina in North America (Hamelin et al 1998a). These differences could be explained by the fact that there are distinct biotypes of G. abietina var.…”

Status of the European race of Scleroderris canker in Canada

“…The hypothesis of several introductions of the disease in Newfoundland was presented earlier (Laflamme 1993). A recent study (Hamelin et al 1998) shows that the introduction of the disease on the island was from a different origin than the introduction on the mainland.…”

“…The introductions into Newfoundland are different fkom the one on the continent (Hamelin et al 1998) with the exception of Ontario where the population study has not yet been done. The EU race was probably introduced from Europe through infected seedlings and multiple introductions have been suggested (Hamelin et al 1996).…”

Alien fungal species on asymptomatic live woody plant material imported into Canada

“…These fungi may not be regulated since they might not possess a scientific name, do not induce signs and symptoms, or have a well-characterized introduction pathway. In the past, the introduction of inconspicuous fungi (and Oomycota) has been responsible for diseases such as chestnut blight, white pine blister rust, scleroderris canker (European race), butternut canker and sudden oak death (Hamelin et al 1998;Et-Touil et al 1999;Dutech et al 2010;Broders & Boland 2011;Goss et al 2011). Due to their inconspicuous nature and the fact that these fungi were generally unknown to science before their introduction into North America, it was difficult in the 20th century for border inspectors to intercept them before their introduction and establishment into our forests.…”