APS Homepage

Poster: Biology & Disease Mgmt: Genetics of Resistance


Screening of Wild Hop (Humulus lupulus) Germplasm for Identification of Resistance to Pseudoperonospora humuli
J. HAVILL (1), A. Orshinsky (1), D. Carter (1), S. Poulose (1) (1) University of Minnesota, U.S.A.

Pseudoperonospora humuli, the causal organism of hop downy mildew, is considered the most economically-damaging pathogen to hop production. Host resistance, in addition to intensive cultural management practices and fungicide use, is the primary control measure. Wild hops (Humulus spp.) are distributed across the North America and Eurasia. They may provide a resource for novel resistance genes and germplasm diversity for local hop breeding programs. Sixteen sites in Minnesota with wild populations of hops were identified. At 14 of these sites individual rhizomes were recovered from 1 – 27 unique individuals. One-hundred six wild and cultivated hop genotypes originating from the USA, England, Japan, and Kazakhstan were screened for foliar resistance to downy mildew (Pseudoperonospora humuli) using a detached-leaf assay. Each genotype was tested with three replicates. In total, 33 genotypes were as resistant as the current commercial standard (cv. ‘Teamaker’) which included five other cultivars, five Japanese hop (H. japonicus) genotypes, two experimental breeding lines, and 21 wild H. lupulus genotypes. We identified two geographically distinct locations in Minnesota containing previously unreported germplasm possessing high levels of foliar resistance that may be useful for breeding locally-adapted varieties. Work is currently underway to characterize the morphological characters and chemical attributes of the hop inflorescences of selected resistant wild plants.