Low genetic diversity suggests the recent introduction of dogwood powdery mildew to North America

Authors: WYMAN, CHRISTOPHER - University Of Tennessee; HADZIABDIC, DENITA - University Of Tennessee; BOGGESS, SARAH - University Of Tennessee; Rinehart, Timothy - Tim; WINDHAM, ALAN - University Of Tennessee; Wadl, Phillip; TRIGIANO, ROBERT - University Of Tennessee

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2019
Publication Date: 5/17/2019
Citation: Wyman, C.R., Hadziabdic, D., Boggess, S., Rinehart, T.A., Windham, A.S., Wadl, P.A., Trigiano, R.N. 2019. Low genetic diversity suggests the recent introduction of dogwood powdery mildew to North America. Plant Disease. https://doi.org/10.1094/PDIS-01-19-0051-RE.
DOI: https://doi.org/10.1094/PDIS-01-19-0051-RE

Interpretive Summary: There is currently limited information on the genetic diversity and population structure of powdery mildew infecting dogwood trees. Because of the apparent infrequency of sexual reproduction, the hypothesis of this study was that powdery mildew reproduces most prominently via conidia and has become essentially a clonal organism in the eastern US. To test this hypothesis species-specific microsatellite loci were developed and utilized to characterize the genetic diversity and population structure of powdery mildew in the eastern U.S.

Technical Abstract: Cornus florida (flowering dogwood) is a popular understory tree endemic to the eastern hardwood forests of the United States (U.S.). In 1996, dogwood powdery mildew caused by Erysiphe pulchra, an obligate, biotrophic fungus of large bracted dogwoods, reached epidemic levels throughout the C. florida growing region. In the late 1990s, both sexual and asexual stages of E. pulchra were regularly observed, but thereafter the teleomorph has been found less frequently. We examined the genetic diversity and population structure of 174 E. pulchra samples growing on C. florida leaves using 15 microsatellite loci. Clone correction analysis reduced the sample size to 97 multilocus haplotypes. Our study indicated both low genetic diversity and lack of definitive structure within the population sampled in eastern U.S. Significant linkage disequilibrium was also observed in seven of eight arbitrary geographically defined subpopulations, implying that predominant means of reproduction was asexually via conidia. This study also showed evidence of a recent population bottleneck among the sampled population. The results of our study inferred a high probability that E. pulchra has become clonal since its advent in 1995, and lends support to the hypothesis that E. pulchra is an exotic pathogen.