EXOPOLYSACCHARIDES IN THE PATHOGENIC INTERACTION OF CLAVIBACTER-MICHIGANENSIS SUBSP MICHIGANENSIS WITH TOMATO PLANTS

The extracellular polysaccharide (EPS) of seven strains of Clavibacter michiganensis subsp. michiganensis, a pathogen of tomato (Lycopersico n esculentum Mill.) was isolated and the carbohydrate composition was determined. Based on the EPS analyses and the interaction with tomato plants the strains could be placed into two groups. Strains of Group I efficiently colonize tomato plants and produce an EPS with an identic al carbohydrate composition with fucose, glucose, galactose in a molar ratio of 2 : 1 : 1. When injected into leaves of four-o'clock (Mirabi lis jalapa L.), a non host plant of C. m. subsp. michiganensis, strain s of Group I induce a hypersensitive-like reaction (HR). In contrast, isolates of Group II are avirulent, do not propagate in tomato and fai led to induce an HR on M. jalapa. These strains produced only small am ounts of EPS in vitro which was distinctly different in composition. A lthough the composition of the EPS in planta was not definitively dete rmined, wilting, the typical disease symptom of tomato caused by C. m. subsp. michiganensis, seems not to depend on EPS production based on two lines of evidence. First, EPS(-) mutants were not altered in virul ence, and second, the natural isolate NCPPB 1574 (Group I) and the pla smid-free cured derivative of NCPPB382, CMM100, did not cause disease although they produced EPS in identical quantities and composition as the virulent strains and effectively colonized tomato plants.