Severe outbreak of bacterial speck, caused by Pseudomonas syringae pv. tomato, on field‐grown tomatoes in the eastern Anatolia region of Turkey

Abstract

In the spring of 1999 and 2000, a serious outbreak of a leaf spot disease was observed on tomato plants grown in commercial fields in the eastern Anatolia region of Turkey. It is thought that low temperature and extensive spring rains encouraged the disease, resulting in approximately 20% yield loss and reduced quality of tomato fruit. Initially, symptoms were small (1–2 mm diameter), water-soaked, dark brown to black spots which developed on young expanding leaves. Later, a number of lesions on older leaves, petioles, stems and fruits enlarged and coalesced, causing leaf desiccation and defoliation. A fluorescent, Gram-negative bacterium was consistently isolated from diseased tissues onto King's B medium. All of the 20 representative strains isolated were oxidase- and arginine dihydrolase-negative, and levan-positive. None of the strains utilized erythritol and l-lactate as the sole carbon source (Jones et al., 1986; Hildebrand et al., 1988). Fatty acid analysis identified the strains as Pseudomonas syringae pv. tomato, with similarity indices ranging from 63 to 94% (Janse et al., 1992). Pathogenicity of the strains was confirmed on 5-week-old tomato seedlings (cv. Easy Harvest) sprayed with bacterial suspensions containing 108 c.f.u. mL−1 sterile water. Inoculated and sterile water-sprayed control plants were covered with polyethylene bags for 48 h at 25°C, then bags were removed and plants were maintained in the greenhouse. Water-soaked spots similar to those observed in the field developed on the inoculated plants within 5–7 days. No symptoms developed on control plants. The bacterium was reisolated from inoculated plants, and identified as strains of Pseudomonas syringae pv. tomato. This is the first report of the occurrence and outbreak of a bacterial speck disease caused by this bacterium on tomato grown in the eastern Anatolia region of Turkey. Although not proven, it is speculated that contaminated seeds and/or transplants may have been the source of introduction of the pathogen to this region. This study was supported by a grant from the Research Funds appropriated to Atatürk University.