1. Department of Plant Genetics, Breeding and Seed Science, China Agricultural University; Beijing Key Laboratory of Crop Genetic Improvement Laboratory of Crop Heterosis and Utilization MOE; Beijing 100193 China
2. College of Grassland Science and Technology China Agricultural University No. 2 Yuanmingyuan West Road, Haidian District Beijing 100193 China
3. Institute of Botany Chinese Academy of Sciences Beijing 100093 China
4. Forage Crop Research Institute Japan Grassland Agricultural and Forage Seed Association 388‐5 Higashiakada, Nasushiobara Tochigi 329‐2742 Japan