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Peer Reviewed

© 2002 Plant Management Network.
Accepted for publication 7 June 2002. Published 11 June 2002.

First Report of Southern Wilt Caused by Ralstonia solanacearum on Geranium in Florida

Prakash M. Pradhanang, M. Timur Momol, Hank Dankers, Esen A. Momol, North Florida Research and Education Center, University of Florida, 155 Research Road, Quincy, FL 32351; and Jeffrey B. Jones, Plant Pathology Department, University of Florida, 2553 Fifield Hall, Gainesville, FL 32611

Corresponding author: Timur Momol.

Pradhanang, P. M., Momol, M. T., Dankers, H., Momol, E. A., and Jones, J. B. 2002. First report of southern wilt caused by Ralstonia solanacearum on geranium in Florida. Online. Plant Health Progress doi:10.1094/PHP-2002-0611-01-HN.

Fig. 1. Bacterial wilt symptoms (wilt and necrotic leaves) of geranium caused by Ralstonia solanacearum (click image for larger view).

During the fall season of 2001, the Florida Extension Plant Diagnostic Clinic at Quincy received ‘Patriot Cherry’ and ‘Patriot Bright Red’ geranium plants (Pelargonium x hortorum) from an ornamental plant producer in Florida. The leaves were wilted and chlorotic (Fig. 1) and the stem base and roots were rotted. When cross sections of the stem base were placed in a tube of clear water, white milky strands of bacterial cells were visible. Ralstonia solanacearum was consistently isolated from the stem bases when plated on semiselective agar (SMSA) (1) and tetrazolium medium (TTC) (3). 

A total of four bacterial strains from individual geranium plants were stored at -80°C. Identification of presumptive R. solanacearum strains was confirmed by whole-cell fatty acid methyl ester analysis (MIDI, Newark, DE) and by polymerase chain reaction (PCR). R. solanacearum specific primers amplified a single 281 bp fragment (2). All strains were typed as biovar 1. 

Pathogenicity tests were conducted on geranium (cv. Miss Scarlett) and ‘Equinox’ tomato (Lycopersicon esculentum) grown in 10-cm pots. Four geranium strains and one tomato strain (Rs 5, biovar 1) were grown in CPG (Casamino acids Peptone Glucose) broth (3) overnight. Plants were inoculated by pouring a 10-ml bacterial suspension (3.5 to 5 x 107 CFU/ml) into the soil after cutting one side of the roots with a sterile scalpel blade. Sterile water was applied to the non-inoculated control plants. Each strain was inoculated on five geranium and five tomato plants. Plants were kept at 27 to 30°C under controlled conditions with a continuous supply of water from the base of the pots. Five days after inoculation both geranium and tomato plants developed wilt symptoms irrespective of the strain inoculated on them. Ten days after inoculation all plants had developed wilt symptoms. The cut end of the stem base or petiole of wilted geranium and tomato plants produced a typical bacterial oozing in clear water. No symptoms developed on non-inoculated control plants, nor was bacterial ooze observed in the cut end of the stem base. R. solanacearum was reisolated from the basal stems of inoculated plants. Identity of the reisolated bacteria was verified with PCR as described earlier.

The ornamental plant producer was visited to assess the intensity of the disease. Several benches of diseased geraniums were observed. Random samples from wilted plants produced the typical oozing in water from the cut end of petioles and produced typical colonies of R. solanacearum on SMSA medium. All sanitation procedures were applied and a total of 60,000 geraniums were destroyed to prevent further infections in the production areas. The total loss was estimated at $80,000.

Southern wilt of geranium was reported in North Carolina in 1981 (4), but the biovar was not identified. To our knowledge, this is the first report of R. solanacearum causing Southern wilt in geranium in Florida. We have established that the pathogen in this case was biovar 1, which is commonly found in the southern United States and South America.

Literature Cited

1. Engelbrecht, M. C. 1994. Modification of a semi-selective medium for the isolation and quantification of Pseudomonas solanacearum. Bacterial Wilt Newsletter 10:3-5.

2. Ito, S., Ushijima, Y., Fujii, T., Tanaka, S., Kameya-Iwaki, M., Yoshiwara, S., Kishi, F. 1998. Detection of viable cells of Ralstonia solanacearum in soil using a semiselective medium and a PCR technique. J. Phytopathol. 146:379-384.

3. Kelman, A. 1954. The relationship of pathogenicity in Pseudomonas solanacearum to colony appearance on a tetrazolium medium. Phytopathology 44: 693-695.

4. Strider, D.L., Jones, R.K., and Haygood, R.A. 1981. Southern bacterial wilt of geranium caused by Pseudomonas solanacearum. Plant Dis. 65:52-53.