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When natives become invasive: population genetic signatures following range expansion in members of thousand cankers disease complex

Denita Hadziabdic: University of Tennessee

<div>Thousand Cankers Disease (TCD) of trees in the Juglandaceae is a consequence of interactions among a fungal pathogen, <em>Geosmithia morbida</em>, an insect vector, <em>Pityophthorus juglandis,</em> and susceptible plant hosts. In the past two decades, TCD has spread from the western to eastern USA, and has invaded the natural range of four North American species of <em>Juglans</em>. It has also spread to Italy where it affects native English walnut (<em>J. regia</em>). Due to the significant potential spread of the pathogen and/or vector, critical information is needed on the population structure of pathogen and vector, pathways for potential dispersal, and host-parasite co-adaptation. In this study, we elucidate diversity patterns and potential pathways of range expansion from the hypothesized center of origin (Arizona and New Mexico) and a secondary center of invasion (California). A total of 807 <em>G. morbida</em> and 1767 <em>P. juglandis</em> individuals from subpopulations in the western USA were genotyped using 16 and 15 species-specific microsatellite loci, respectively. Our preliminary results indicate generally high genetic diversity, presence of population structure, and evidence of gene flow among subpopulations. High levels of genetic diversity across all groups may be explained by human-mediated movement of infested plant material from multiple sources and on multiple occasions. Our findings support an earlier hypothesis that the pathogen and vector have long been associated in the southwestern USA.</div>