1. Department of Plant Genetics, Breeding and Seed ScienceChina Agricultural University; Beijing Key Laboratory of Crop Genetic Improvement; Laboratory of Crop Heterosis and UtilizationMOE; Beijing 100193China
2. Key Laboratory of Plant ResourcesInstitute of BotanyChinese Academy of SciencesBeijing 100093China
3. Inner Mongolia Research Centre for PractacultureChinese Academy of SciencesBeijing 100093China
4. University of Chinese Academy of SciencesBeijing 100049China
5. Forage Crop Research InstituteJapan Grassland Agricultural and Forage Seed Association388‐5 HigashiakadaNasushiobaraTochigi 329‐2742Japan