VIEW ARTICLE

Cytology and Histology

Early Proliferation and Migration and Subsequent Xylem Occlusion by Erwinia amylovora and the Fate of its Extracellular Polysaccharide (EPS) in Apple Shoots. Charles G. Suhayda, Department of Plant Pathology, University of Missouri, Columbia 65201, Present address of the senior author: DOE/MSU Plant Research Laboratory, East Lansing, MI 48824; R. N. Goodman, Department of Plant Pathology, University of Missouri, Columbia 65201. Phytopathology 71:697-707. Accepted for publication 12 December 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-71-697.

Growth in intercellular space of a virulent isolate of Erwinia amylovora injected into shoot tissue of the susceptible apple cultivar Jonathan is limited to the wound site during the initial 48 hr after inoculation. During this period, systemic proliferation and migration of the pathogen occurs detectably only in mature annular and helical vessels. Occlusion of the vessels is caused by a dense fibrillar material associated with the presence of bacteria and is believed to be largely bacterial extracellular polysaccharide (EPS). Absorption of EPS by cut bases of apple shoots results in vessel occlusion similar to that seen in tissue infected by bacteria. Our electron micrographs indicate that the site of early bacterial proliferation and systemic migration is in mature xylem vessels rather than in the cortex and pith as reported in the earlier literature.