1. Institute of Crop Sciences, Key Lab. of Crop Physiology and Ecology, Chinese Academy of Agricultural Sciences Ministry of Agriculture and Rural Affairs Beijing 100081 P. R. China
2. College of Resources and Environmental Sciences China Agricultural Univ. Beijing 100193 P. R. China
3. Maize Research Inst. Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences Hohhot 010031 P. R. China
4. College of Agronomy Inner Mongolia Agricultural Univ. Hohhot 010031 P. R. China