ARS | Publication request: QTL Mapping of Powdery Mildew Susceptibility in Hop (Humulus lupulus L)

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2010
Publication Date: June 22, 2011
Citation: Henning, J.A., Townsend, M.S., Gent, D.H., Bassil, N.V., Matthews, P., Buck, E., Beaston, R. 2011. QTL Mapping of Powdery Mildew Susceptibility in Hop (Humulus lupulus L). Euphytica. 180:411-420.

Interpretive Summary: Hop powdery mildew is serious pathogen reducing both yield and quality in hop producing regions of USA and Europe. Producers use numerous pesticide applications to control this disease. The most economical and environmentally friendly way to control disease is growing resistant varieties. Recent evidence in other crop species supports selection for absence of susceptibility to fungal pathogens as a more durable resistance mechanism. The objective of this study was to identify molecular markers associated with susceptibility to powdery mildew in hop. Statistical analysis of the molecular markers used in this study resulted in identifying three regions on the two separate hop chromosomes that were linked to expression of plant resistance to powdery mildew. The region on linkage group C7 had both additive and dominant effects upon controlling phenotype expression. The presence or absence of the two molecular markers bordering this region on linkage group C7 defined susceptibility in offspring. This is the first report in hop identifying molecular markers linked to QTLs associated with disease susceptibility.

Technical Abstract: Hop powdery mildew is best controlled via the production of resistant varieties. Recent evidence supports selection for absence of susceptibility to fungal pathogens as a more durable resistance mechanism. The objective of this study was to identify molecular markers associated with susceptibility to powdery mildew in hop. Parents and offspring from the cross designed to test for susceptibility were clonally replicated and inoculated with powdery mildew in an experiment run under greenhouse conditions in Corvallis, OR. DNA was extracted, purified and analyzed via three different marker systems. Analysis of the resulting markers was based upon the “two-way pseudo-testcross” procedure. Statistical analysis of the molecular markers resulted in three regions on the hop chromosomes that were linked to expression of plant resistance to powdery mildew. The region on linkage group C7 had both additive and dominant effects upon controlling phenotype expression. The presence or absence of the two molecular markers bordering the region on linkage group C7 defined susceptibility in offspring. This is the first report in hop identifying molecular markers linked to QTLs associated with disease susceptibility.