Characterization of a Gene Cluster that Specifies Pathogenicity in Erwinia stewartii. D. L. Coplin. Department of Plant Pathology, The Ohio State University, Columbus 43210-1087 U.S.A. R. D. Frederick, D. R. Majerczak, and L. D. Tuttle. Department of Plant Pathology, The Ohio State University, Columbus 43210-1087 U.S.A. MPMI 5:81-88. Accepted 24 October 1991. Copyright 1992 The American Phytopathological Society.

A large cluster of pathogenicity genes from Erwinia stewartii DC283 was cloned in cosmid pES1044. These genes (wts) are required for both water-soaked lesion formation and wilting on corn seedlings. The wts region spanned 14 kb and was mapped by Tn5 and Tn3HoHoI mutagenesis of pES1044 followed by introduction of selected mutations into the chromosome of DC283. Two chromosomal deletion mutants of the wts region, DM3001 and DM3020, were isolated. Trans complementation analysis identified three complementation groups in the map order wtsA, wtsC, and wtsB. wtsA, wtsB, and wtsC functions were not required for initial growth of the bacteria in corn seedlings; final populations of the wts mutants were only slightly lower than that of the parental strain. DM3001 wtsB persisted in infected plants and was recovered from the leaves and stalks 6 wk after inoculation. wtsA::lacZ and wtsB::lacZ gene fusions were expressed in planta and in a minimal-salts glucose medium amended with casamino acids or yeast extract.