PLP PhD Candidate Thesis defense seminar: Lexi Heger ANOTHER DAY, ANOTHER SPORE TO TRAP
February 9, 2026 1:30PM - 2:30PM
ADVANCING MOLECULAR DETECTION, AEROBIOLOGY, AND GENETIC RESISTANCE DISCOVERY TO PLASMOPARA VITICOLA AND OTHER GRAPEVINE PATHOGENS
Room A 271
For ZOOM please contact Talya Esquivel
Members of the Examining Committee and their Department:
- Timothy Miles – Plant, Soil and Microbial Sciences/ Molecular Plant Sciences Program
- Martin Chilvers – Plant, Soil and Microbial Sciences
- Rachel Naegele – Plant, Soil and Microbial Sciences/ Molecular Plant Sciences Program/ Sugarbeet and Bean Research Unit USDA-ARS, East Lansing, MI
- Walter Mahaffee – Horticulture Crops Disease and Pest Management Research Unit, USDA-ARS, Corvallis, OR
ABSTRACT
Grapevine production in Michigan faces persistent pressure from fungal and oomycete pathogens favored by humid environmental conditions, particularly downy mildew (Plasmopara viticola), botrytis bunch rot (Botrytis cinerea), and powdery mildew (Erysiphe necator). This dissertation integrates molecular detection, aerobiological monitoring, and a genome wide association study to investigate these pathogens in Michigan vineyards. A multiplexed qPCR assay capable of differentiating three cryptic species of P. viticola using a unique mitochondrial locus was developed. The assay demonstrated high sensitivity and specificity and showed compatibility with digital PCR, providing a novel tool for pathogen detection and population monitoring. Three air-sampling technologies were used for simultaneous detection of P. viticola, B. cinerea, and E. necator in a small vineyard plot over two growing seasons. A multiplexed qPCR assay for the three pathogens showed that pathogen capture varied by sampler type but rarely by sampler height, with notable differences among pathogens, highlighting limitations and opportunities for improving airborne inoculum monitoring. Lastly, a study combining multi-year field phenotyping with rhAmpSeq genotyping and genome-wide association analyses in an interspecific F1 grapevine population was used to detect disease resistance loci. Disease severity traits displayed strong interannual variability, resulting in year-specific SNP associations and supporting a quantitative, environmentally responsive resistance architecture. Novel associations for downy mildew and botrytis bunch rot were identified, emphasizing the contribution of novel minor-effect loci. Collectively, this work advances tools for pathogen detection and provides new insights into the genetic and environmental complexity of disease resistance in grapevine, informing future breeding and disease management strategies.
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