Disease Note

Outbreak of Bacterial Stem Rot of Geranium in Minnesota. B. W. Kennedy, Department of Plant Pathology, University of Minnesota, St. Paul 55108. F. L. Pfleger, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 70:78. Accepted for publication 3 September 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-78a.

During 1983 and 1984, several industrial greenhouse firms reported heavy losses (in excess of 100,000 plants) from a disease that appeared as water-congested leaf spots in early spring and subsequently resulted in systemic infection and death of geranium (Pelargonium hortorum Bailey). Source of original plants was not determined; all commonly propagated cultivars appeared to be susceptible. The slow-growing bacterium, presumably belonging in the genus Xanthomonas, produced a nonwater-soluble, pale yellow pigment and copious slime on a sugar-rich medium. The pathogen was easily isolated on nutrient agar and readily became systemic and killed plants when 5 Μl of a suspension containing 1 × 10⁸ cfu/ml was placed on severed leaf midveins. The bacterium survived at least 20 wk in infected debris on soil surfaces in the greenhouse. Continuous light or a 19-hr day photoperiod did not enhance disease development over a 14-hr day regime at 27–32 C and thus was not helpful in detecting latent infection in suspect plants.