1. Saskatoon Research Centre, Agriculture and Agri-Food Canada, Saskatoon, Saskatchewan S7N 0X2, Canada
2. University of Guelph, Guelph, Ontario N1G 2W1, Canada
3. John Innes Centre, Norwich NR4 7UH, United Kingdom and
4. Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706