Class I and Class II avrD Alleles Direct the Production of Different Products in Gram-Negative Bacteria. I. Yucel. Department of Plant Pathology, University of California, Riverside 92521. S. L. Midland, J. J. Sims, and N. T. Keen. Department of Plant Pathology, University of California, Riverside 92521 U.S.A. MPMI 7:148-150. Accepted 1 October 1993. Copyright 1994 The American Phytopathological Society.