Induction of resistance to Clavibacter michiganensis subsp michiganensis

Tomato plants pre-inoculated with the avirulent strain NCPPB 3123 of Clavib acter michiganensis subsp. michiganensis (Cmm) were protected largely again st challenge infection by virulent strains of Cmm. Effectiveness of this pr otective effect was mainly dependent on the inoculation sites, the bacteria l cell concentration used for pre- and challenge inoculations, and the: tim e interval between both inoculations. This defence reaction was systemic an d stable throughout the whole growing season. Resistance can also be induce d by pre-inoculation of heat-killed bacteria or application of isolated EPS of the strain 3123. Strain 3123 spreads out in tomato plants in the same m anner as virulent Cmm isolates, but its colonization of tomato fruits and s eeds was substantially lower. Papillary to spherical electron dense particl es were observed at the tonoplast in parenchyma cells of the vascular syste m of tomato plants inoculated with the strain 3123. Numerous investigations carried out to examine the ability of 3123 to induce resistance in other h ost/pathogen-systems showed that it was only specific for tomato/Cmm.