1. Labortory of Genetics, University of Wisconsin, Madison, WI 53706, USA
2. Syngenta Biotechnology Inc., 3054 Cornwallis Road, Durham, NC 27709, USA
3. Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093, USA
4. Present address: Instituto de Ecologia, Universidad Nacional Autónoma de México (UNAM), AP-Postal 70-275, Coyoacán 04510,México DF, Mexico
5. Crop Genetics Research, Pioneer-A DuPont Company, 7300 NW 62nd Avenue,Johnston, IA 50131, USA