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.