In planta - complementation of Clavibacter michiganensis subsp sepedonicusstrains deficient in cellulase production or HR induction restores virulence

Clavibacter michiganensis subsp. sepedonicus, a Gram positive bacterium tha t causes bacterial ring rot of potato, was studied in eggplant, an alternat e host, using strains that differed in phenotype. Two factors affecting vir ulence, the ability to induce a hypersensitive response (HR) and cellulase production, were studied. A plasmid-free isolate of C. michiganensis subsp. sepedonicus that causes HR on tobacco but is unable to produce cellulase m ultiplied efficiently in planta, but caused only weak symptoms. In contrast , a strain that is unable to induce HR on tobacco but produces cellulase wa s impaired in the ability to multiply in the host and caused no symptoms. W hen the two non-virulent strains were coinoculated into eggplants, typical disease symptoms developed. This enhancement was not due to formation of a new phenotype or significant increases in population density of either of t he strains. Our results suggest that both cellulase production and the abil ity to induce HR are required for a successful infection process and diseas e induction by C. michiganensis subsp. sepedonicus. Our results additionall y suggest that the ability to induce HR on non-host plants is required for multiplication in the host plant, whereas cellulase expression is necessary for induction of disease symptoms.