1. International Food Policy Research Institute 2033 K Street, N.W. Washington DC 20006‐1002
2. Dep. of Agricultural and Resource EconomicsUniv. of California Giannini Hall 207 Berkeley CA 94720‐3310
3. Dep. of Agricultural and Resource EconomicsUniv. of California Davis CA 95616‐8512
4. Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) Apartado 6‐641 06600 Mexico DF Mexico