Pathogenic Behavior of Several Mini-Mu-Induced Mutants of Erwinia chrysanthemi on Different Plants. Carole Beaulieu. Département de Biologie Moléculaire, Université Libre de Bruxelles, B1640 Rhode St-Genèse, Belgium. Frédérique Van Gijsegem. Département de Biologie Moléculaire, Université Libre de Bruxelles, B1640 Rhode St-Genèse, Belgium.. MPMI 5:340-346. Accepted 10 April 1992. Copyright 1992 The American Phytopathological Society.

Insertion mutagenesis with Mu dIIPR3 as mutator agent and subsequent screening of the mutants on Pisum sativum identified virulence factors in Erwinia chrysanthemi strain 3937. Seven mutants showing reduced virulence on pea were isolated. These mutants were characterized by three different phenotypes: deficiency in secretion of pectate lyases and endoglucanases; reduction of growth in minimal media; and lack of a 40-kDa outer membrane protein. Using four plant species, we assessed the virulence of these mutants and of previously derived Mu dIIPR3 mutants with insertions in plant-inducible genes. The mutant with reduced growth in minimal media showed reduced virulence only on one host plant. Mutants defective in the export of pectate lyases and endoglucanases showed reduced virulence on all host plants tested. Most mutants with alterations in plant-inducible genes and the mutant with a 40-kDa outer membrane protein showed reduced virulence on all host plants tested except potato tuber. Other mutants in plant-inducible genes were reduced in virulence on one or two host plants, were as virulent as the wild type, or were supervirulent on specific hosts.