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June 19, 2003
Source: British Soc Plant Pathol, NEW DISEASE REPORTS, Vol. 7 [edited]

First report of Pseudomonas viridiflava on melon in Turkey
Y Aysan <aysanys@mail.cu.edu.tr>, M Mirik, O Cinar (Department of Plant Protection, Faculty of Agriculture, Cukurova University, 01330 Balcali, Adana, Turkey); A Ala, F Sahin (Department of Plant Protection, Faculty of Agriculture, Ataturk University, 25240 Erzurum, Turkey). Accepted for publication 06/05/03

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 the eastern Mediterranean region of Turkey. A number of water-soaked lesions were first observed on the undersides of the cotyledons. 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 about 10 per cent and some of the infected seedlings in the nursery evntually died. The disease 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 10 representative strains isolated were aerobic, rod shaped, Gram negative, oxidase and arginine dihydrolase negative, and catalase and pectolytic positive. The bacterial strains did not produce levan type colonies on sucrose nutrient agar, but were able to induce a hypersensitive reaction on tobacco leaves. The strains were capable of producing acid from sorbitol, 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_ [Pv] with similarity indices ranging from 59 to 89 per cent (Janse et al, 1992).

Pathogenicity of the strains was confirmed on melon seedlings (cv. Nun) by needle inoculation of bacterial suspensions containing 100 million CFU (colony forming units) per mL in 0.85 per cent saline. Saline was used as negative control. The plants were maintained in the controlled climate room for a week at 25 C and 70 per cent relative humidity (RH).

Pv was reisolated from the inoculated plants and is identical to the original strain (GSPB 1685, obtained from Gottingen, Germany) on the basis of fatty acid analysis. Water-soaked lesions and leaf necrosis, similar to those observed in the nursery, developed on the inoculated plants within 5 to 7 days. No symptoms developed on control plants. To date there is only a single previous report of melon as host of Pv from Greece (Goumans & Chatzaki, 1998). This is the first report of the occurrence of Pv causing
bacterial leaf spot and necrosis on melon in Turkey.

References:
Goumans DE, Chatzaki AK. Characterization and host range evaluation of Pseudomonas viridiflava from melon, blite, tomato, chrysanthemum and eggplant. European Journal of Plant Pathology 1998; 104: 181-8.
Janse JD, Derks JHJ, Spit BE, van der Tuin WR. Classification of fluorescent soft rot Pseudomonas bacteria, including P. marginalis strains, using whole cell fatty acid analysis. Systematic and Applied Microbiology 1992; 15: 538-53.
King EO, Ward MK, Raney DE. Two simple media for the demonstration of pyocyanin and fluorescin. Journal of Laboratory Clinical Medicine 1954; 44: 301-7.

[Pv is basically a weak, opportunistic pathogen with a varied natural host range (including pear, bean, cauliflower, cabbage, sweet pepper, pea and canola). In onion, Pv causes severe damage and post-harvest damage during storage can also be very high. -Mod.DH]