Pathogenic Behavior of Pectinase-Defective Erwinia chrysanthemi Mutants on Different Plants. Carole Beaulieu. Département de Biologie moléculaire, Université Libre de Bruxelles, 1640 Rhode St-Genèse, Belgium. Martine Boccara(2), and Frédérique Van Gijsegem(1). (1)Département de Biologie moléculaire, Université Libre de Bruxelles, 1640 Rhode St-Genèse, Belgium, and (2)Laboratoire de Pathologie végétale, Institut National Agronomique Paris-Grignon, F-75231 Paris Cedex 05, France.. MPMI 6:197-202. Accepted 30 November 1992. Copyright 1993 The American Phytopathological Society.

The pathogenic behavior of Erwinia chrysanthemi strain 3937 and of several pectinase-defective mutants was analyzed on four different plants. The DeltaPel mutant displayed a reduced virulence on all host plants tested. However, the individual pel and pem genes had, within host plants, a differential role in pathogenicity. On Saintpaulia ionantha, the genes of the pelADE cluster and the pem gene were essential for a full expression of E. chrysanthemi virulence, whereas the genes of the pelBC cluster did not seem to be involved in pathogenicity. On pea, only the PelA¯ mutant exhibited a reduced virulence, and a mutant deleted of all the pel genes except pelA (PelBCDE¯) was as virulent as the wild-type strain. On chicory leaf, the pem gene and all the pel genes except pelE were needed for virulence. On potato tuber, only the Pem¯ mutant showed a reduced virulence. In addition to PLa, PLb, PLc, PLd, and PLe, we showed that another set of pectinases was produced in planta. Pectinases present in macerated tissues varied within host plants. This study brings strong evidence for a contribution of the different enzymes to the wide host range of strain 3937.