1. Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, 1432 Ås, Norway
2. Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, and Norwegian Institute for Agricultural and Environmental Research, Høgskoleveien 7, 1432 Ås, Norway
3. Department of Plant and Environmental Sciences, Norwegian University of Life Sciences
4. Norwegian Institute for Agricultural and Environmental Research, Ås
5. Department of Plant Pathology and Plant-Microbe Biology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456