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Wild hops - New genetic resources for resistance to hop powdery mildew (Podosphaera macularis ssp. humuli)
Seigner, E. , Lutz, A. and Felsenstein, F.G.

Hop powdery mildew is a serious disease of hop causing a dramatic drop of yield and quality on susceptible hop varieties. The most effective and economic way of controlling powdery mildew on hop can be achieved by using resistant varieties in commercial hop production. Just from the beginning of all breeding efforts at the Hop Research Center Hll, emphasis has been put on the development of hop cultivars with a broad range of resistance to all major diseases. Over the last 15 years the main focus in breeding has been to improve resistance to hop powdery mildew (PM) in Hll breeding lines and new cultivars. Extensive studies on the virulence spectrum of powdery mildew populations had revealed that all hop resistance genes currently known were overcome by virulent strains of PM occurring in the hop growing regions of the Hallertau, England, France, and the USA. Thus, for hop breeding it was urgently needed to look for new sources of resistance which were expected to be found in wild hops. Since 2001 more than 15,000 wild hops from throughout the world have been screened in the greenhouse for PM resistance. Subsequently, resistant individuals were retested in the laboratory using the detached leaf assay and afterwards in the fields under natural infection conditions. In this way 54 very promising wild hops were identified showing resistance to all virulent PM strains currently known. Resistant individuals will be used as crossing partners in our breeding programs to broaden the genetic basis for PM resistance in the Hll hop germplasm.

Descriptors: Humulus lupulus, hop powdery mildew, wild hop germplasm, resistance

BrewingScience - Monatsschrift fr Brauwissenschaft, 59 (July/August 2006), pp. 122-129