1. College of Forest Resources, University of Washington, Seattle, Washington 98195
2. Department of Horticulture, Oregon State University, Corvallis, Oregon 97331
3. School of Natural Resources, Ohio Agricultural Research and Development Center, Ohio State University, Wooster, OH 44691
4. Flanders Interuniversity Institute for Biotechnology, University of Gent, B-9000 Gent, Belgium