1. College of Agronomy; Northwest A&F Univ.; Yangling Shaanxi 712100 China
2. College of Life Sciences; Northwest A&F Univ.; Yangling Shaanxi 712100 China
3. State Key Lab. of Crop Stress Biology in Arid Areas (Northwest A&F Univ.); Yangling 712100 Shaanxi China
4. Crop Research Institute; Drnovska 507 Prague 6 161 06 Czech Republic
5. Dep. of Agronomy; Kansas State Univ.; Manhattan KS 66506