First report of Pseudomonas viridiflava on melon in Turkey

In February 2003, a severe disease with bacterial leaf necrosis symptoms was observed on container-grown melon (Cucumis melo cv. Nun) seedlings at a nursery in Adana, located in eastern Mediterranean region of Turkey. A number of water-soaked lesions were first observed on the undersides of the cotyledons (Fig. 1). Small, dark brown and angular leaf spots were subsequently observed on the true leaves at later stages of the disease. Disease incidence was estimated as approximately 10%. Some of infected seedlings in the nursery finally died. The diseased resulted in the rejection of 10,000 transplants from the nursery. These symptoms were consistent with those of the disease described by Goumans & Chatzaki (1998). A fluorescent, opaque, semifluid, gram-negative bacterium was isolated from diseased tissues onto King's medium B (King et al., 1954). All ten representative strains isolated were aerobic, rod shaped, gram negative, oxidase and arginin dihydrolase negative, catalase and pectolytic positive. The bacterial strains did not produce levan type colonies on sucrose nutrient agar, but were able to induce hypersensitive reaction on tobacco leaves. The strains were capable of producing acid from sorbitole, fructose, glucose, L (+) arabinose, D (+) xylose, D (-) mannitol, but not from sucrose, trehalose, maltose, melibiose, lactose and D (-) arabinose. Utilisation of D (-) tartrate was positive. Fatty acid analysis identified the strains as Pseudomonas viridiflava with similarity indices ranging from 59 to 89 % (Janse et al., 1992).

Pathogenicity of the strains was confirmed on melon seedlings (cv. Nun) with needle inoculation of bacterial suspensions containing 10⁸ CFU per ml in 0.85% saline. Saline was used as negative control. The plants were maintained in the controlled climate room for a week at 25°C and 70% RH. The bacterium was reisolated from the inoculated plants and characterised as identical to the original strain (GSPB 1685, obtained from Gottingen, Germany) on the basis of Fatty acid analysis. Water-soaked and leaf necrosis symptoms, similar to those observed in the nursery, developed on the inoculated plants within 5 to 7 days (Fig. 2). No symptoms developed on control plants. To date there is only a single previous report of melon as host of Pseudomonas viridiflava from Greece (Goumans & Chatzaki, 1998). This is the first report of the occurrence of Pseudomonas viridiflava causing bacterial leaf spot and necrosis on melon in Turkey.