1. U. S. Department of Agriculture, Agricultural Research Service, Plant Protection Institute, Beltsville, Maryland 20705
2. National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20014
3. Station de Physiologie et de Biochimie Végétales, Centre de Recherches de Bordeaux, Institut National de la Recherche Argonomique, 33, Pont-de-le Maye, France