1. Universidad Autonoma Chapingo Chapingo Mexico
2. Biometrics and Statistics Unit, CIMMYT Apdo. Postal 6‐641 06600 Mexico DF Mexico
3. Dep. of Agronomy and Plant Genetics Univ. of Minnesota 1991 Upper Buford Cir. St Paul MN 55109
4. Global Maize Breeding Program, CIMMYT Apdo. Postal 6‐641 06600 Mexico DF Mexico