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, China
2. Beijing Vegetable Research Center (BVRC), Beijing Academy of Agriculture and Forestry Science (BAAFS), Beijing, China
3. Key Laboratory of Biology and Genetic Improvement of Horticultural Crops North China, Ministry of Agriculture, Beijing, China
4. Department of Grassland Science, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing, China
5. Forage Crop Research Institute, Japan Grassland Agricultural and Forage Seed Association, 388-5 Higashiakada, Nasushiobara, Tochigi, Japan