|Gent, David - Dave|
|CLAASSEN, BRIANA - Oregon State University|
|TWOMEY, MEGAN - Oregon State University|
|WOLFENBARGER, SIERRA - Oregon State University|
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2018
Publication Date: 9/20/2018
Citation: Gent, D.H., Claassen, B.J., Twomey, M.C., Wolfenbarger, S.N. 2018. Identification of resistance to powdery mildew in publically-available male hop germplasm. Plant Health Progress. 19(3):258-264. https://doi.org/10.1094/PHP-05-18-0027-RS.
Interpretive Summary: The most efficient means to manage plant diseases often involves growing plant varieties that are genetically resistant. Host resistance is a desirable trait in hop for the disease powdery mildew, but limited resistance is available presently in cultivated varieties because the pathogen that causes the disease has overcome extant sources of resistance. In this research we conducted an extensive evaluation of male hop germplasm in the U.S. Department of Agriculture collection for novel sources of resistance to powdery mildew. After multiple rounds of selection for resistance, 12 individuals were identified that did not develop disease when challenged with multiple strains of the fungus from the U.S. and Europe. Identification of possible novel sources of resistance to powdery mildew will be useful to hop breeding programs in the western U.S. and elsewhere, eventually yielding new varieties that will require less inputs to be produced.
Technical Abstract: Powdery mildew (caused by Podosphaera macularis) is one of the most important diseases of hop in the western U.S. Strains of the fungus virulent on cultivars possessing the resistance factor termed R6 and the cultivar Cascade have become widespread in the Pacific Northwestern U.S., the primary hop producing region in the country, rendering most cultivars grown susceptible to the disease at some level. In an effort to identify potential sources of resistance in extant germplasm, 136 male accession of hop contained in the U.S. Department of Agriculture collection were screened under controlled conditions. Iterative inoculations with three isolates of P. macularis with varying race identified 23 (16.9%) accessions with apparent resistance to all known races of the pathogen present in the Pacific Northwest. Of the 23 accessions, 12 were resistant when inoculated with three additional isolates obtained from Europe that possess novel virulences. The nature of resistance in these individuals is unclear, but does not appear to be based on known R genes. Identification of possible novel sources of resistance to powdery mildew will be useful to hop breeding programs in the western U.S. and elsewhere.