Occurrence of Bacterial Fruit Blotch of Watermelon Caused by Acidovorax avenae subsp. citrulli in the Eastern Mediterranean Region of Turkey.

Abstract

Turkey has the second highest production level of watermelon (Citrullus lanatus L.) in the world, with 3.8 million tons produced in 2005. In the spring of 2005, a severe outbreak of a disease resembling bacterial fruit blotch was observed on watermelon cv. Crispy growing in a production area of 35,000 ha in Adana Province in the eastern Mediterranean Region of Turkey. In 13 commercial watermelon fields surveyed in this study, incidence of symptomatic fruit ranged from 30 to 45%. Characteristic symptoms were dark, gray-green stains or blotches on the surface of fruits. Cracks developed in the rind and released an amber-colored substance. Bacteria were consistently isolated from affected fruits and they formed nonfluorescent colonies on King's medium B. Identification of isolated bacterial strains was based on the methods described by Schaad et al. (2). All strains were oxidase positive, gram negative, arginine dyhydrolase negative, and produced a hypersensitive response on tobacco leaves (Nicotiana tabacum cv. Samsun). Strains were identified as Acidovorax avenae subsp. citrulli (1,2) on the basis of the results of biochemical tests (1,2) and sole carbon substrate utilization (BIOLOG GN; Biolog Inc., Hayward, CA) with 75 to 93% similarity indices. A pathogenicity test was performed for nine identified strains by injecting a bacterial suspension (108 CFU/ml of saline) under the rind of three harvested watermelon (cv. Diyarbakir) fruits and into the stems of three seedlings. Saline was used as the negative control. The fruits and seedlings inoculated with each strain were incubated in polyethylene bags for 48 h at 25°C. Dark green water-soaked lesions developed on inoculated fruits and water-soaking and stem necrosis were observed on the seedlings 3 to 5 days after inoculation. The bacterium was readily reisolated from inoculated fruits and seedlings and identified as A. avenae subsp. citruli on the basis of BIOLOG GN. In 1995, bacterial fruit blotch of watermelon has been observed and eradicated in the Marmara Region of western Turkey (1). Therefore, to our knowledge, this is the first outbreak of bacterial fruit blotch on watermelon in the eastern Mediterranean Region of Turkey.