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ABSTRACT The powdery mildew fungusErysiphe quercicola(Erysiphaceae) has a complex taxonomic history that has long complicated assessments of its geographic distribution and host associations. Although knowledge of the global host range of this species has expanded substantially over the past two decades, sequencing‐confirmed records from North America remain scarce, and despite its recognition as an introduced pathogen, the timing of introduction and the geographic extent and host range ofE. quercicolain the United States are poorly understood. In this study, herbarium specimens ofE. quercicolafrom North America, spanning both historical and contemporary collections, were examined using molecular phylogenetic approaches. Specimens collected from multipleQuercusspecies across several regions of the United States, as well as from related hosts within theFagaceae, were evaluated. Sequence data confirm the presence ofE. quercicolain North America onQuercusspecies based on herbarium specimens collected as early as 1944, as well as on mango (Mangifera indica;Anacardiaceae) in Florida from material collected in 1935. These records raise the possibility of historical introduction pathways associated with cultivated hosts, potentially from the horticulturally important mango tree (M. indica); however, additional multilocus phylogenetic analyses and host range inoculation experiments will be required to determine whether powdery mildew populations infecting mango andQuercusin North America represent the same lineage. Additional sequencing‐confirmed records document the species on multiple native oak species representing different sections ofQuercusincludingQ. bicolor,Q. gambelii,Q. garryana,Q. geminata,Q. kelloggii,Quercus × jolonensisandQ. macrocarpaas well as onNotholithocarpus densiflorus. Together, these findings clarify the long‐term presence ofE. quercicolain the United States, expand knowledge of its North American host range, and demonstrate the value of herbaria for reconstructing the invasion history of forest pathogens.
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Introgression, Phylogeography, and Genomic Species Cohesion in the Eastern North American White Oak Syngameon
ABSTRACT Hybridization and interspecific gene flow play a substantial role in the evolution of plant taxa. The eastern North American white oak syngameon, a group of approximately 15 ecologically, morphologically and genomically distinguishable species, has long been recognised as a model system for studying introgressive hybridization in temperate trees. However, the prevalence, genomic context and environmental correlates of introgression in this system remain largely unknown. To assess introgression in the eastern North American white oak syngameon and population structure within the widespreadQuercus macrocarpa, we conducted a rangewide survey ofQ. macrocarpaand four sympatric eastern North American white oak species. Using a Hyb‐Seq approach, we assembled a dataset of 3412 thinned single‐nucleotide polymorphisms (SNPs) in 445 enriched target loci including 62 genes putatively associated with various ecological functions, as well as associated intronic regions and some off‐target intergenic regions (not associated with the exons). Admixture analysis and hybrid class inference demonstrated species coherence despite hybridization and introgressive gene flow (due to backcrossing of F1s to one or both parents). Additionally, we recovered a genetic structure withinQ. macrocarpaassociated with latitude. Generalised linear mixed models (GLMMs) indicate that proximity to range edge predicts interspecific admixture, but rates of genetic differentiation do not appear to vary between putative functional gene classes. Our study suggests that gene flow between eastern North American white oak species may not be as rampant as previously assumed and that hybridization is most strongly predicted by proximity to a species' range margin.
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- Award ID(s):
- 2129281
- PAR ID:
- 10639156
- Publisher / Repository:
- Molecular Ecology
- Date Published:
- Journal Name:
- Molecular Ecology
- ISSN:
- 0962-1083
- Page Range / eLocation ID:
- e17822
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/mec.17822
