Dissertation
INSIGHTS INTO THE GENETIC DIVERSITY, POPULATION STRUCTURE, AND FUNGICIDE SENSITIVITY OF THE APPLE POWDERY MILDEW PATHOGEN PODOSPHAERA LEUCOTRICHA IN THE UNITED STATES
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000005433
Handle:
https://hdl.handle.net/2376/121856
Abstract
Apple powdery mildew, caused by Podosphaera leucotricha, is a constant threat to apple production worldwide. In this study, a first whole genome (43.8 Mb) of P. leucotricha was obtained and used to study the genetic diversity and spatial genetic structure in 253 isolates hierarchically sampled in 2018 and 2019 from 10 apple orchards in Washington, Virginia, and New York. Microsatellite genotyping, based on 15 novel simple sequence repeat loci, revealed a total of 83 multilocus genotypes (MLGs), most of which were unique to specific orchard populations. Differentiations among P. leucotricha isolates grouped either by State of origin and orchards in Washington were significant (P <0.001) and accounted for 83% and 12% of the total variation observed, respectively. A Bayesian cluster analysis showed heterogeneity between orchards and grouped Washington P. leucotricha isolates into four different genetic groups, each represented by different groups of MLGs. Random mating analyses indicated that U.S. P. leucotricha populations are clonal during the growing season, although evidence of sexual reproduction is presented. None of the most frequent P. leucotricha MLGs found in surveyed U.S. orchards were virulent on a resistant apple genotype carrying the major mildew resistance gene Pl-1. Furthermore, 232, 217, and 240 P. leucotricha isolates, collected from organic and conventional orchards, were tested for their sensitivity to the fungicides trifloxystrobin, triflumizole, and boscalid, respectively. Effective concentrations inhibiting 50% growth (EC50) were not significantly different (P > 0.05) between baseline (organic) and exposed (conventional) populations, although some isolates showed higher EC50 values. This reduced sensitivity in P. leucotricha was not associated with specific mutations known to confer resistance in other plant-pathogenic fungi, providing another evidence that actual resistance has not emerged in U.S. commercial orchards. Findings from this study will facilitate future research in this biotrophic pathogen, as well as the monitoring of fungicide resistance and the distribution and spread of pathogen genotypes to achieve a sustainable control of apple powdery mildew in the Pacific Northwest and other apple-growing regions.
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Details
- Title
- INSIGHTS INTO THE GENETIC DIVERSITY, POPULATION STRUCTURE, AND FUNGICIDE SENSITIVITY OF THE APPLE POWDERY MILDEW PATHOGEN PODOSPHAERA LEUCOTRICHA IN THE UNITED STATES
- Creators
- Lederson Ganan Betancur
- Contributors
- Achour Amiri (Advisor)Tobin L Peever (Advisor)Katherine M Evans (Committee Member)Timothy D Murray (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Plant Pathology
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 145
- Identifiers
- 99900599457401842
- Language
- English
- Resource Type
- Dissertation