- Agronomic: hops
- Crop Production: plant breeding and genetics, varieties and cultivars
- Natural Resources/Environment: biodiversity
- Pest Management: genetic resistance
In 2016 112 wild hop accessions were screened for their response to Pseudoperonospora humuli, the causal organism of hop downy mildew and a obligate parasite of hops. These 112 accessions originated from private collections or USDA-sponsored collection trips and encompassed the native distribution of hop within North America. Private collections were made from multiple locations within Minnesota, Michigan, Wisconsin, and Vermont. Additionally, USDA-collected materials originated from Kazahkstan, Manitoba and Sakatchewan, CA, and Arizona, Colorado, Missouri, New Mexico, and North Dakota.
Preliminary experiments indicated that botanical varieties significantly differ in their tolerance to hop downy mildew, which may be related to exposure to environmental factors that are conducive for the establishment of the disease in a field setting and not directly to their ability to tolerate infection. Continued experiments with a larger collection indicated there are significant overlaps in tolerance to hop downy mildew across botanical varieties, indicating that resistance or tolerance may be independent of climatic factors and primarily composed of genetic factors.
In 2017, assessments of the sub-sampled germplasm collection were completed by using a whole plant inoculation method. Individual plants from the sub-sampled collection were selected based on geographic origin, presumed genetic diversity (based on geographic origin), and their respective response to infection by P. humuli. Additionally, we demonstrate that for the purposes of breeding downy mildew tolerant or resistant lines, use of foliar assessments may be indicative of field performance in the future based on correlation analysis of publicly available phenotypic data.
- Collect wild hop germplasm for phenotypic evaluation
- Screen wild hop germplasm for downy mildew resistance