First Record of Clavibacter michiganensis subsp. michiganensis Causing Canker of Tomato Plants in Syria

Abstract

Between March and mid April of 2007, several extensive surveys for Clavibacter michiganensis subsp. michiganensis were carried out among greenhouses in the coastal strip provinces of the Mediterranean Sea in north-west Syria (Latakia and Tartous), where a large proportion of Syrian fresh-market tomatoes are produced. This bacterium causes bacterial canker of tomato and is considered an A2 quarantine pathogen by the European Plant Protection Organization (EPPO). It is currently present in all major tomato-production areas in the EPPO region (4), but has not been previously reported in Syria. The survey revealed typical canker symptoms in 7% of 150 inspected greenhouses that contained cvs. Dima, Huda, and Astona. These symptoms included stunting, dark brown-to-black lesions on the leaf margins, wilting and defoliation of whole plants, and vascular discoloration. The disease incidence in such greenhouses was estimated at 15% at the time of the survey. Diseased plants were surface sterilized and homogenized in sterile water. Serial dilutions were plated on nutrient glucose agar. Suspected colonies were further purified by repeated restreaking on new agar plates. All 10 of the suspected strains obtained from different locations were identified as C. michiganensis subsp. michiganensis on the basis of the following observations: bacterial cells of all strains had a coryneform shape, were nonmotile, gram positive according to Gram's reaction test with 3% KOH (2), oxidase-negative, and caused hypersensitive reactions on leaves of Mirabilis jalaba (1) within 24 h. PCR assays were conducted with the C. michiganensis subsp. michiganensis-specific primer set PSA-4/R (3) and template DNA prepared from in-vitro-grown bacteria with the MasterPure Gram Positive DNA Purification Kit (Epicentre Biotechnologies, Madison, WI). The expected 270-bp amplicon was observed for both reference strains as well as the Syrian strains. Pathogenicity of the strains was confirmed by artificial inoculation of 6-week-old tomato plants (Lycopersicon esculentum Mill. cv. Lyconorma). Inoculation was performed by stabbing the stem with a sterile needle through a drop (~35 μl) of bacterial suspension (~108 CFU/ml in 0.01 M MgSO4) placed in the axil of the second or third true leaf. Three tomato seedlings were inoculated with each strain. Control plants were inoculated with sterile 0.01 M MgSO4. Symptoms including lateral wilt of leaflets, stem lesions, and wilting of whole plants were observed within 10 to 15 days after inoculation, except for the negative control. To fulfill Koch's postulates, reisolation and reidentification of the pathogen was conducted as previously described. To our knowledge, this is the first record of the occurrence of bacterial canker of tomato in Syria. References: (1) R. D. Gitaitis. Plant Dis. 74:58, 1990. (2) T. J. Gregersen. Appl. Microbiol. Biotechnol. 5:123, 1978. (3) K. H. Pastrik and F. A. Rainey. J. Phytopathol. 147:687, 1999. (4) I. M. Smith and L. M. F. Charles, eds. Map 253 in: Distribution Maps of Quarantine Pests for Europe. EPPO/CABI, 1998.