1. Maize Research Institute, Key Laboratory of Crop Genetic Resources and Improvement, Ministry of Education; Sichuan Agricultural University; Xinkang 36, Ya'an Sichuan 625014 China
2. Institute of Crop Breeding and Cultivation, CAAS; Beijing 100081 China
3. International Maize and Wheat Improvement Center (CIMMYT); Apdo 6-641 06600 Mexico D.F. Mexico