1. Department of Plant Sciences, University of California Davis , One Shields Ave, Davis, CA 95616 , USA
2. International Maize and Wheat Improvement Center (CIMMYT) , Carretera México-Veracruz, El Batán, 56130 Texcoco, Edo. de México , México
3. Biostatistics Unit, Institute of Crop Science, University of Hohenheim , Stuttgart 70599 , Germany