1. College of Biology Sciences, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100094, China
2. Key Laboratory of Crop Gene Resources and Germplasm Enhancement, Ministry of Agriculture, National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China
3. United States Department of Agriculture, Agricultural Research Service, Western Regional Research Center, 800 Buchanan Street, Albany, CA 94710, USA