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Disease Note

Outbreak of Black Spot of White Clover Caused by Pseudomonas andropogonis in North Carolina. S. C. Nelson, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. C. L. Campbell, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 75:537. Accepted for publication 6 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0537F.

Plants of white clover (Trifolium repens L. 'Regal' and Southern Regional Virus Resistant germ plasm) were transplanted into four plots in a 10-ha pasture of white clover and tall fescue (Festuca arundinacea Schreb.) near Ra[eigh, North Carolina, in May [990. Inky-black, round to angular, often vein-delimited lesions with watersoaked margins and yellow halos appeared on clover foliage in midJune. By 20 Ju[y, 81% of the 512 plants had symptoms varying in severity from small, water-soaked lesions to complete necrosis and defoliation of infected leaves. Microscopic examination of diseased tissue in aqueous mounts revealed the flow of bacteria from the edges of lesions. Colonies characteristic of nonfluorescent pseudomonads were isolated from lesions and used to fulfill Koch's postulates. The pathogen was identified presumptively by fatty acid methyl ester assay (MIDI Microbial Identification System, 0.63 on the Similarity Index) as Pseudomonas andropogonis (Smith) Stapp. A[though Jones et a[ (1) reported a similar disease near Raleigh caused by P. syringae van Hall (P. trifoliorum (Jones, Williamson, Wolf, and McCullough) Stapp), this is the first report of P. andropogonis as a pathogen of white clover in North Carolina.

Reference: (1) L. R. Jones et al. J. Agric. Res. 12:471, 1923.