|ISHS Acta Horticulturae 668: I International Humulus Symposium
BREEDING FOR POWDERY MILDEW RESISTANCE IN HOP (HUMULUS L.): STRATEGIES AT THE HOP RESEARCH CENTER, HUELL, GERMANY
|E. Seigner, A. Lutz, H. Radic-Miehle, S. Seefelder, F.G. Felsenstein
|Humulus lupulus, Podosphaera macularis, wild hops, genetic engineering, marker assisted selection
Hop breeding at Huell, Germany was established 75 years ago to provide cultivars adapted to the needs of growers and brewers.
In recent years, severe damage caused by powdery mildew (Podosphaera macularis formerly called Sphaerotheca humuli) intensified the need for breeding efforts to improve resistance of hop cultivars.
Extensive investigations revealed that almost all currently utilized sources of resistance in classical breeding have been overcome by recently evolved races of powdery mildew throughout Europe and the USA. Thus, screening wild hops from various regions of the world for effective new resistance genes has been started.
Assays designed to select for hop powdery mildew (PM) resistance are being conducted in both the greenhouse, following artificial inoculation with PM spores, and in the lab using a detached leaf system in combination with single spore isolates with known virulence behavior.
The efficiency and reliability of testing for powdery mildew resistance in hop can be increased significantly by using molecular markers.
Currently, closely associated molecular markers are being identified for various genes conferring resistance to this fungal disease.
Marker assisted pyramiding of these resistance genes is one of our long-term breeding objectives.
In addition, work continues on evaluating the potential of genetic engineering in hop breeding.
A transformation method has been successfully established by transferring selection markers and reporter genes into hop cultivars by Agrobacteria. Transgenic plants of ‘Saazer’ are being cultivated in the greenhouse, showing stable expression.
Recently, a resistance gene has been transferred into cv. ‘Saazer’ and ‘Hallertauer Mittelfrueh’. First tests on stable gene expression and resistance performance in ‘Saazer’ plants were conducted.
Various strategies using classical and molecular breeding techniques are demonstrated as being useful to improve powdery mildew resistance in new hop cultivars.
Ultimately, these at endeavors at Huell will contribute towards developing a cost-effective and environmentally-friendly production of hop.
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