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Dispersal of Verticillium albo-atrum in the Xylem of Alfalfa. Barbara W. Pennypacker, Research Associate, Department of Plant Pathology, Pennsylvania State University. K. T. Leath, Research Plant Pathologist, U.S. Regional Pasture Research Laboratory, USDA, ARS, University Park, PA 16802. Plant Dis. 67:1226-1229. Accepted for publication 12 May 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-1226.

Alfalfa plants (Medicago sativa L. ‘Saranac’) were inoculated with spores of Verticillium albo-atrum and grown in slant-board culture in a growth chamber. Plants were examined histologically at 4-day intervals until permanent leaf wilt and defoliation occurred. Eight days after root-dip inoculation, the fungus had colonized the entire stem. V. albo-atrum was found only in the xylem vessel elements, where it sporulated freely. Germinated spores were frequently observed in these vessels. In serial isolations from newly regrown stems from field-grown plants, V. albo-atrum was noncontinuous in the host stem during early stages of colonization. Based on histological evidence and isolation data, we concluded that internal sporulation was the mechanism facilitating rapid colonization of the host by V. albo-atrum.

Keyword(s): lucerne.