Effects of Temperature, Plant Age, Inoculum Concentration, and Cultivar on the Incubation Period and Severity of Bacterial Canker of Tomato. R. J. Chang, Department of Plant Pathology, University of Illinois, Urbana 61801. S. M. Ries, and J. K. Pataky. Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 76:1150-1155. Accepted for publication 3 June 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1150.

The incubation period and severity of bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis were influenced by temperature, plant age, inoculum concentration, and cultivar. The incubation period was longer and symptom development was less severe with cooler temperatures, older plants, lower concentrations of inocula, and moderately resistant cultivars. The time required before leaves wilted or cankers developed at the edge of inoculated petioles varied from 12 to 34 days, depending on conditions. Symptoms developed fastest on 2-wk-old susceptible seedlings grown at 25 C and inoculated with 8 × 10⁸ cfu/ml. Similar factors affected the length of incubation period and severity of bacterial canker. The optimum conditions for appearance of symptoms also favored development of severe symptoms.