Abstract
White pine blister rust is caused by the fungal pathogen Cronartium ribicola J.C. Fisch (Basidiomycota, Pucciniales). This invasive alien pathogen was introduced into North America at the beginning of the 20th century on pine seedlings imported from Europe and has caused serious economic and ecological impacts. In this study, we applied a population and landscape genetics approach to understand the patterns of introduction and colonization as well as population structure and migration of C. ribicola. We characterized 1,292 samples of C. ribicola from 66 geographic locations in North America using single nucleotide polymorphisms (SNPs) and evaluated the effect of landscape features, host distribution, and colonization history on the structure of these pathogen populations. We identified eastern and western genetic populations in North America that are strongly differentiated. Genetic diversity is two to five times higher in eastern populations than in western ones, which can be explained by the repeated accidental introductions of the pathogen into northeastern North America compared with a single documented introduction into western North America. These distinct genetic populations are maintained by a barrier to gene flow that corresponds to a region where host connectivity is interrupted. Furthermore, additional cryptic spatial differentiation was identified in western populations. This differentiation corresponds to landscape features, such as mountain ranges, and also to host connectivity. We also detected genetic differentiation between the pathogen populations in natural stands and plantations, an indication that anthropogenic movement of this pathogen still takes place. These results highlight the importance of monitoring this invasive alien tree pathogen to prevent admixture of eastern and western populations where different pathogen races occur.
Highlights
Invasive fungal pathogens of trees represent a global threat to natural forests and tree plantations, resulting in economic losses and, in some cases, changes to ecosystem functions and a reduction in biodiversity [1,2,3]
Fisch (Basidiomycota, Pucciniales) causes white pine blister rust, a disease that affects all white pines (Pinus subsection Strobus). This invasive alien pathogen was introduced into North America and discovered at the beginning of the 20th century on pine seedlings imported from Europe and planted for reforestation in the USA and Canada
Colonization history and host distribution influence white pine blister rust populations The structure of North American C. ribicola populations is strongly influenced by geographic origin, with longitudinal and latitudinal patterns
Summary
Invasive fungal pathogens of trees represent a global threat to natural forests and tree plantations, resulting in economic losses and, in some cases, changes to ecosystem functions and a reduction in biodiversity [1,2,3]. C. Fisch (Basidiomycota, Pucciniales) causes white pine blister rust, a disease that affects all white pines (Pinus subsection Strobus). Fisch (Basidiomycota, Pucciniales) causes white pine blister rust, a disease that affects all white pines (Pinus subsection Strobus) This invasive alien pathogen was introduced into North America and discovered at the beginning of the 20th century on pine seedlings imported from Europe and planted for reforestation in the USA and Canada. It can cause mortality rates approaching 100% in high hazard zones and has severely reduced survival, natural regeneration and reforestation efforts with white pines in North America [5,6,7]
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