Developmental and Structural Section
Frederick, Lafayette , Salters, Armstead L. , Chen, Dillion .
Xylem Dysfunction in Elms Induced by the Dutch Elm Disease Pathogen Ophiostoma ulmi.
Studies have been conducted on the wilting mechanism associated with the Dutch elm disease (DED) syndrome. Water deficits in leaves of elms (Ulmus spp.) appear to be responsible for wilting of leaves and death of infected trees. We have postulated, based on separate nodal vasculature studies in elms, that the anatomical site crucial to unimpeded movement of water from stem to leaves of diseased plants is at the juncture of the leaf-stem axis. A histological study has been conducted, therefore, on xylem dysfunction at the nodes of twigs from diseased plants and in cuttings exposed to culture filtrates of the DED pathogen. The effect of culture filtrates on tracheary elements in twig and nodal cuttings of the DED resistant elm, U. pumila, has also been made. In both naturally diseased and culture filtrate treated cuttings of the American elm extensive xylem dysfunction has been found in leaf and petiolar traces. Dysfunction observed includes extensive vessel wall discoloration and distortion; incipient tylose formation; discoloration of tracheary parenchyma; erosion of the inner surface of vessel walls; and conspicuous occluding of vessel lumina by translucent substances in unfixed sections and granular substances in similar fixed sections. In culture filtrate treated cuttings of the American elm xylem dysfunction was evident within 6 hours after exposure. Complete occlusion of a majority of vessels in leaf and petiolar traces, accompanied by wilting, occurred within 48 hours. By contrast, leaves on similar cuttings from the Chinese elm lacked manifestations of wilting and xylem dysfunction. Evidence from these observations suggest that leaf wilt in DED primarily results from the development of extensive occlusions in the nodal region of twigs and that this dysfunction is induced by pathotoxins of the pathogen as it grows in infected areas of the xylem.
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1 - Howard University, Department of Biology, 415 College Street Northwest, Washington, DC, 20059, USA
2 - Charles Gideons Elementary School, Office of the Principal, 897 Welch St. SW, Atlanta, GA, 30310
3 - Howard University, Biology, Washington, DC, 20059
Dutch elm disease
Presentation Type: Poster:Posters for Sections
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM