Abstract
1Departamento de Genética Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Apdo Postal 565-A, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
2Soybean and Alfalfa Research Laboratory, Agricutural Research Service, US Department of Agriculture, Beltsville, MD 20705, USA
3College of Agriculture and Natural Resources, The Department of Natural Resource Sciences and Landscape Architecture, University of Maryland, College Park, MD 20742, USA
4Department of Microbiology, College of Biology, Beijing Agricultural University, Beijing 100094, People's Republic of China
5CIEH, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, México