SURVIVAL AND DISSEMINATION OF CLAVIBACTER-MICHIGANENSIS SUBSP MICHIGANENSIS IN TOMATOES

Rifampicin-resistant strains of Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker of tomato, were used to investigate the dynamics of epiphytic populations and overwintering survival of the pathogen. Epiphytic populations stabilized at 10(6)-10(8) cfu per leaflet and 10(5)-10(6) cfu per green fruit. After log(10) transformation, epiphytic populations of the pathogen on leaflets and fruit approached a normal distribution. C m. michiganensis survived for at least 24 mo in infested debris at the soil surface, but for only 7 mo in buried debris. Infested debris that was allowed to overwinter served as primary inoculum for establishment of epiphytic populations of C m. michiganensis on a subsequent processing-tomato crop. These plants became diseased and their yields were significantly reduced. The establishment of epiphytic populations of the pathogen and local survival can be important in the disease cycle of bacterial canker.