R. Nissinen et al., In planta - complementation of Clavibacter michiganensis subsp sepedonicusstrains deficient in cellulase production or HR induction restores virulence, EUR J PL P, 107(2), 2001, pp. 175-182
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.