585 Geographical Distribution of Clavibacter michiganensis subsp. michiganensis in Serbia S. Milijasevic, B. Todorovic, E. Rekanovic, I. Potocnik, M. Stepanovic and B. Duduk Pesticide and Environment Research Institute Banatska 31B P.O. Box 163 11080 Belgrade – Zemun Serbia Keywords: Clavibacter michiganensis subsp. michiganensis, tomato, disease incidence, geographical distribution Abstract During 2006 and 2007, an extensive survey for the canker pathogen was conducted in the major tomato growing districts in Serbia (Leskovac, Lebane, Padinska Skela, Sabac, Trstenik, Ub, Stara Pazova, Cacak) in order to estimate the infested area and disease incidence. Sixty bacterial strains were isolated from the diseased leaves, stems, fruits and seeds with dilution plating on the nonselective (NA, NBY) and semiselective media (D 2 ANX, mSCM and mCNS). The investigated strains were identified as C. michiganensis subsp. michiganensis based on biochemical characteristics, hypersensitive response in four-o’clock plant leaves and pathogenicity test on tomato seedlings. Amplification of DNA fragments of 614 bp in the first PCR protocol and DNA fragments of 270 bp in the second, confirmed that the investigated strains belonged to C. michiganensis subsp. michiganensis. The first wilt and canker symptoms were recorded in greenhouses in southern Serbia, in June 2006 on tomato cvs. ‘Belle’ and ‘Magnus’. Further survey of greenhouse and field grown tomatoes in 2006 and 2007 resulted in additional findings of the disease in three other tomato growing regions in greenhouses on tomato cvs. ‘Delfine’ and ‘Trogir’ and in one region on the field grown tomato cv. ‘Hector’. Disease incidence in greenhouses ranged from 2 to 50% while it reached 100% in the field, resulting in heavy losses. However, in spite of the fact that the results of these investigations showed the geographical distribution of C. michiganensis subsp. michiganensis in Serbia, further monitoring of this pathogen in tomato crops is neccesary considering its quarantine status. INTRODUCTION Bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis is one of the most serious bacterial diseases, both in the field and greenhouse tomato production worldwide. Bacterial canker is a vascular and parenchymatal disease with a wide range of symptoms which include necrosis of the leaf margin, stunting, wilting, vascular discoloration and eventual plant death. The pathogen also induces leaf-spots as a result of local infection, as well as small, raised, superficial necrotic spots on the fruit surrounded by white halos, referred to as “bird’s eye lesions” (Gitaitis, 1990; EPPO/CABI, 2005). Crop losses due to the vascular infection are usually substantial and marketable fruit quality is poor (Chang et al., 1992; Gitaitis, 1990; Hadas et al., 2005). In Serbia, this pathogen is on the A2 list of pests regulated as quarantine, since 1957, when it was first described (Sutic, 1957) and it has not posed a serious threat to tomato production in Serbia for more than fifty years. However, during tha past few years severe outbreaks of the disease were recorded in greenhouse tomato production (Milijasevic et al., 2006, 2007). Therefore, the objective of this study was to survey tomato crops for the canker pathogen both in greenhouses and fields in major tomato growing regions in Serbia in order to confirm the pathogen identity and to estimate the infested area and disease incidence. Proc. IV th Balkan Symp. on Vegetables and Potatoes Eds.: L. Krasteva and N. Panayotov Acta Hort. 830, ISHS 2009