1. State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University; Taicheng Road 3 Yangling Shaanxi 712100 China
2. Agricultural Research Service, United States Department of Agriculture and Department of Plant Pathology; Washington State University; Pullman WA 99164-6430 USA
3. East Malling Research; New Road, East Malling Kent ME19 6BJ UK