An Outbreak of Bacterial Stem Rot of Dieffenbachia amoena Caused by Erwinia carotovora subsp. carotovora in the Eastern Mediterranean Region of Turkey.

Severe outbreaks of bacterial stem rot disease occurred on dieffenbachia plants (Dieffenbachia amoena cv. Tropic Snow) during the autumn and spring seasons of 2002 and 2003 in two commercial glasshouses (3.5 ha) near Adana and Mersin in the Eastern Mediterranean Region of Turkey. Characteristic symptoms of the disease were wilting of the lower leaves, darkening and water soaking of the leaves and stem at or below the soil level, and browning in the vessel and pith of the diseased plants. Eventually, the stem and leaves completely rotted, and the plants collapsed. Nearly 30 and 40% (2002 and 2003, respectively) of the 20,000 potted plants in the glasshouses were destroyed because of the disease. Cuttings often developed a typical soft rot during propagation. Disease incidence was estimated at approximately 50% on propagating material during 2003. Isolations were made from rotted stems, leaves, and discolored vessels of the dieffenbachia plants on King's medium B. Bacteria consistently isolated from the diseased tissues formed white-to-cream colonies on the medium. Bacteria from purified colonies were gram, oxidase, and arginine dyhidrolase negative, catalase positive, and facultative anaerobic. Ten representative strains all fermented glucose and reduced nitrates to nitrites. The strains caused soft rot of potato slices within 24 h at 25°C. All strains were resistant to erythromycin in an antibiotic disk (15 µg) assay. Negative results were obtained from utilization of α-methyl glycoside, reducing substance from sucrose, and indole production from tryptophane and phosphathase activity. Positive results were obtained from pectate, aesculin, and gelatine liquefaction for all strains. Acid was produced from glucose, sucrose, mannitol, mannose, lactose, raffinose, melibiose, trehalose, and L(+)-arabinose but not Darabinose, sorbitol, inulin, and maltose. Pathogenicity was confirmed by needle-stab inoculation at the stem on three plants each of dieffenbachia and tomato plants (5-week-old cv. H-2274). Sterile distilled water was used as a negative control. All plants were covered with polyethylene bags for 48 h at 25°C. Within 72 h after inoculation, water-soaking and soft-rot symptoms were observed on dieffenbachia and tomato plants. All of the bacterial strains isolated in the present study were identified as Erwinia carotovora subsp. carotovora (Jones) based on fatty acid methyl ester analysis with similarity indices ranging from 80 to 94%. Furthermore, Biolog GN (Department of Plant Protection, Faculty of Agriculture, Ataturk University, Erzurum, Turkey) profiles identified them as the same pathovar with similarity values of 67 to 72%. All of the test results were similar to those of reference strain GSPB 435 (Gottinger Sammlung phytopathogener Bakterien, Georg-August University, Gottingen, Germany) of E. carotovora subsp. carotovora used in this study. To our knowledge, this is the first report of the occurrence and outbreak of a bacterial rot disease on dieffenbachia grown in the Eastern Mediterranean Region of Turkey. Contaminated cuttings may be the primary source of inoculum within and between glasshouses.

Watermelon as a New Host of Pseudomonas viridiflava, Causal Agent of Leaf and Stem Necrosis, Discovered in Turkey.

Severe leaf and stem necrosis symptoms were observed on watermelon seedlings (Citrullus lanatus cv. Euroca) in Adana, Turkey during a warm and humid period in January 2004. Streak-plate isolations were made from leaf and stem lesions on King's medium B. A fluorescent, yellowish mucoid, gram-negative, and oxidase-, levan- and arginin dihydrolase-negative bacterium was consistently isolated from diseased plant samples. All seven representative strains isolated were pectolytic on potato slices and hypersensitive reaction positive on tobacco leaves. The result of LOPAT tests and morphology of the strains were different from Pseudomonas syringae pathovars. The strains produced acid from sorbitol, fructose, glucose, L (+) arabinose, D (+) xylose, D (-) mannitol, but not from D (+) sucrose, trehalose, maltose, melibiose, lactose, and D (-) arabinose. Utilization of D (-) tartrate was positive. Incubation was at 28°C, and the results of the tests were evaluated 7 days after inoculation. Fatty acid analysis (Ataturk University, Erzurum, Turkey) confirmed the bacterial strains as P. viridiflava with a similarity index of 83 to 86% (3). The strains were pathogenic on watermelon, melon, and tomato plants with needle inoculation of bacterial suspensions containing 108CFU ml-1 in a 0.85% saline. Water-soaking and stem necrosis symptoms were observed on the inoculated plants 5 to 7 days after inoculation. The bacterium was readily reisolated from inoculated plants and identified as strains of P. viridiflava, which has been previously reported as a pathogen of melon grown in Turkey (1) and Greece (2). To our knowledge, this is the first study demonstrating the occurrence and outbreak of leaf and stem necrosis disease caused by P. viridiflava on watermelon in the world. References: (1) A. Aysan et al. Plant Pathol. 52:800, 2003. (2) D. E. Goumans and A. K. Chatzaki. Eur. J. Plant Pathol. 104:181, 1998. (3) J. D. Janse et al. Syst. Appl. Microbiol. 15:538, 1992.