Induction of resistance to bacterial pathogens in the pathosystem tomato/Clavibacter michiganensis subsp michiganensis II. Characterization of the resistance inductor

Comparing investigations of the avirulent resistance-inducing Clavibacter m ichiganensis subsp. michiganensis (Cmm) strain NCPPB 3123 and of virulent C mm strains showed differences in the DNA-profile and in the composition of the extracellular polysaccharides (EPS), The strain 3123 grew on agar as ro ugh colonies with less EPS production. These EPS had a smaller portion of f ucose compared to EPS of virulent strains and also showed a resistance-indu cing effect like the bacterial cells. However, in planta no differences wer e observed between strain 3123 and virulent Cmm strains in the mode of spre ad and invasion of distinct tissue areas. Papillary to spherical electron-d ense particles were observed at the tonoplast and at membranes of cell orga nelles in parenchyma cells of the vascular system of tomato plants inoculat ed with the strain 3123. We believe these membrane-associated particles are produced as a defense response to the pre-inoculation with strain 3123.