VIEW ARTICLE

Cytology and Histology

Histopathology of Mimosa Infected with Fusarium oxysporum f. sp. perniciosum. P. M. Phipps, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, Present address of the senior author: Department of Plant Pathology, North Carolina State University, P.O. Box 5397, Raleigh 27607; R. J. Stipes, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061. Phytopathology 66:839-843. Accepted for publication 23 January 1976. DOI: 10.1094/Phyto-66-839.

Proliferation of the Fusarium wilt pathogen, Fusarium oxysporum f. sp. perniciosum, in naturally-infected mimosa tree (Albizia julibrissin) tissues was studied during disease development. Once infection occurred in the roots, the pathogen invaded shoot tissues via the vessel elements of the latest growth ring. Microconidia were found in vessels lacking mycelium, which suggested that they move in the transpiration stream. Gum deposits appeared first in pit apertures of vessel elements, then increased and completely coated or occluded xylem vessels at the time of wilt symptoms. Abundant mycelial growth occurred in vessel elements of wilted trees, and hyphae invaded vasicentric and ray parenchyma cells via pit apertures. Using the ray parenchyma system, the pathogen invaded laterally into all parts of branches and twigs. Subsequent to defoliation, the pathogen emerged from the host through lenticels in the bark on the surface of which it produced sporodochia bearing masses of macroconidia.