An Outbreak of Bacterial Speck Caused by Pseudomonas syringae pv. tomato on Tomato Transplants Grown in Commercial Seedling Companies Located in the Western Mediterranean Region of Turkey

Abstract

A serious outbreak of a leaf spot disease was observed on tomato transplants grown in commercial seedling companies in southwestern Turkey (Antalya) during the springs of 2002 and 2003. Disease incidence was more severe in the western Mediterranean Region of Turkey. Occurrence of the outbreak resulted in approximately 20 and 25% seedling losses in the springs of 2002 and 2003, respectively. The initial symptoms consisted of pronounced water-soaked, dark brown-to-black spots on young expanding leaves that were 1 to 2 mm in diameter. Later, a number of leaf spots on older leaves enlarged and coalesced, causing leaf desiccation and finally, seedling death. In addition, in 2003 the disease incidence was approximately 5% in 142 commercial greenhouses. Tomato production was unaffected since significant outbreaks did not occur on greenhouse plants. No fruit symptoms were observed. Twenty-six strains were isolated from diseased tomato seedlings and plants from different greenhouses located in different places and all were gram negative and fluorescent on King's B medium. All strains were levan and gelatin liquefaction positive and oxidase and arginine dihydrolase negative. None of the 26 strains utilized erythritol and l-lactate as the sole carbon source (1,2). Fatty acid analysis identified the strains as Pseudomonas syringae pv. tomato with similarity indices ranging from 0.876 to 0.932%. Pathogenicity of the isolates was confirmed on 4-week-old tomato seedlings (cv. Biotek Selin) sprayed with the bacterial suspensions containing 108 CFU/ml of sterile water. Later, a number of leaf spots on the leaves enlarged and coalesced, causing leaf desiccation. Inoculated and control tomato seedlings were covered with polyethylene bags and placed in a growth chamber at 25°C for 48 h and then the bags were removed. Small (1 to 2 mm), water-soaked, dark brown-to-black spots similar to those observed in the greenhouses of commercial seedling companies and commercial greenhouses that produce tomato developed on the young expanding leaves of inoculated plants within 7 to 10 days. No symptoms developed on control plants. The bacterium was reisolated from inoculated plants and identified as a strain of Pseudomonas syringae pv. tomato. Koch's postulates were fulfilled. To our knowledge, this is the first report for the occurrence and outbreak of the bacterial speck disease on tomato transplants in greenhouses of commercial tomato seedling production companies in Turkey. References: (1) D. C. Hildebrand et al. Pages 60–80 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. N. D. Schaad, ed. The American Phytopathological Society, 1988. (2) J. B. Jones et al. Plant Dis. 70:151, 1986.