Submitted to: Fungal Genetics Reports
Publication Type: Abstract Only
Publication Acceptance Date: 12/15/2009
Publication Date: 3/1/2009
Citation: Bergemann, S.E., Baumgartner, K. 2009. THE ORIGIN AND MAINTENANCE OF GENETIC DIVERSITY WITHIN POPULATIONS OF THE ROOT PATHOGEN ARMILLARIA MELLEA IN NORTH AMERICA. Fungal Genetics Reports. 56S:403. Interpretive Summary: Armillaria mellea (Basidiomycota, Physalacriaceae) sensu stricto is a common root pathogen of fruit crops, timber trees, and ornamentals in western N. America, Europe, and Asia. However, its rare association with these same hosts in eastern N. America suggests that A. mellea within N. America is not a single species. Comparisons of DNA sequences suggest that western and eastern groups evolved from different ancestors. To determine where these ancestors originated from, 90 fungal strains were characterized with various molecular markers [tri- and tetra-repeat microsatellite loci, Glyceraldehyde 3-phosphate dehydrogenase (GPD), ATP synthase subunit 6 (ATP6)]. Lack of significant ATP6 differences among eastern N. American and European isolates, coupled with results of analyses of GPD, suggest a recent division between populations of A. mellea in eastern N. America and Europe. In western N. America, ATP6 differences reveal two distinct haplotypes present in multiple geographic locations, but GPD analyses do not support an ancient division between strains with either ATP6 haplotype. The origins of A. mellea populations in eastern and western N. America, therefor, appear to be inconsistent with expected biogeographic patterns of continental land masses.
Technical Abstract: Armillaria mellea (Basidiomycota, Physalacriaceae) sensu stricto is a common root pathogen of fruit crops, timber trees, and ornamentals worldwide. Phylogenetic analyses of nuclear rDNA and protein-coding loci support differentiation of four geographic groups: Asia, western N. America, eastern N. America and Europe. In N. America, western and eastern groups evolved from different ancestors, but their diversification from alternate ancestors has not been examined. To estimate origin, timing, and diversification from ancestral populations, 90 isolates were genotyped with tri- and tetra-repeat microsatellite loci, and haplotypes were constructed from nuclear and mitochondrial genes (Glyceraldehyde 3-phosphate dehydrogenase; GPD, ATP synthase subunit 6; ATP6). Lack of significant ATP6 sequence divergence among eastern N. America and European isolates, coupled with results of phylogenetic analyses of GPD, suggests a recent split inconsistent with continental connectivity. Eastern N. American populations show high levels of population admixture, although they are genetically structured across northern and southern regions. In western N. America, ATP6 sequence divergence shows two divergent haplotypes present in multiple populations, but GPD analyses do not support an ancient split. Introgression of both ATP6 haplotypes in western N. America, and the origin and extent of genetic diversity in eastern and western N. America appears to be inconsistent with expected biogeographic patterns of continental land masses.