Bacterial Ring Rot of Potatoes Caused by Clavibacter michiganensis subsp. sepedonicus in Lithuania

Bacterial ring rot of potato (Solanum tuberosum L.) was observed for the first time in Lithuania from 1998 to 1999. The disease, caused by Clavibacter michiganensis subsp. sepedonicus, is considered one of the most important bacterial diseases of potato. Nearly all countries that produce potatoes report the presence of the bacterium (1). C. michiganensis subsp. sepedonicus is listed as an A2 quarantine pathogen by the European and Mediterranean Plant Protection Organization. The pathogen has a latent period that can last for several generations of potato production, thus increasing the risk for further dissemination of the disease. Plant wilting and tuber rotting, characteristic symptoms of the disease, were observed in various localities in Lithuania. The disease was found in 12 potato varieties. Disease incidence approached 5% in the field and 5 to 21% in storage. The presence of C. michiganensis subsp. sepedonicus in diseased as well as asymptomatic plant tissue was determined by immunofluorescence cell staining and enzyme-linked immunosorbent assay with the use of monoclonal and polyclonal antibodies, respectively. More than 350 potato samples were tested. Twenty-five samples tested positive by these methods. Pathogenicity tests of 30 samples were conducted on eggplant. Characteristic symptoms were found on 21 plants. The bacteria were reisolated on nutrient dextrose agar medium from 12 inoculated eggplants. For confirmation of six suspicious strains, polymerase chain reaction with a specific Cms50 primer set was employed (2). In three cases, positive results were obtained. References: (1) I. M. Smith and L. M. F. Charles, eds. 1998. Distribution of Maps of Quarantine Pests for Europe. CAB International, Wallingford, U.K. (2) D. Mills et al. Phytopathology 87:853, 1997.