1. International Maize and Wheat Improvement Center (CIMMYT) Apdo. Postal 6-641, C.P. 06600, D.F., Mexico and Department of Soil and Crop Sciences, Texas A&M University, College Station 77843
2. CIMMYT
3. Department of Soil and Crop Sciences, Texas A&M University
4. Campo Experimental Valle de Mexico INIFAP, Apdo. Postal 10, 56230 Chapingo, Edo. de Mexico, Mexico