VIEW ARTICLE

The Occurrence and Cause of Cavitation of American Elm Shoot Nodal Tissue Infected by Ceratosystis ulmi. W. E. MacHardy, Research Associate and C. H. Beckman, Professor, Department of Plant Pathology-Entomology, University of Rhode Island, Kingston, 02881. Phytopathology 64:290-293.

The cause and nature of cavites observed in infected shoot nodes and the relationship between this nodal cavitation and foliar wilt development were examined.  Cavitation occurred in thin-walled pith parenchyma tissue that is highly sensitive to drying conditions.  Cavitation was induced experimentally by infection with C. ulmi, by desiccation, and by exposure to hydrolyzing enzymes produced in vitro by C. ulmi followed by desiccation.  Nodal cavitation is not essential to foliar wilting.  Cavitated shoot nodes were never noted prior to foliar wilting, and shoots bearing wilted leaves did not always have "pocketed" nodes.  Vessels bordering cavities remained functional.  The presence within vessel elements of culture filtrate containing hydrolyzing enzymes did not interfere with dye movement into leaves.