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Relation of Age of Plants, Temperature, and Inoculum Concentration to Bacterial Canker Development in Resistant and Susceptible Lycopersicon spp.. R. L. Forster, Graduate Fellow, Department of Plant Pathology, North Carolina State University, Raleigh 27607; E. Echandi, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27607. Phytopathology 63:773-777. Accepted for publication 3 January 1973. DOI: 10.1094/Phyto-63-773.

Plants of bacterial canker-resistant Lycopersicon hirsutum (P.I. 251305), L. esculentum (P.I. 340905), and L. esculentum × L. pimpinellifolium (‘MR 4’ and ‘Bulgaria 12’) and of susceptible L. esculentum (‘Manapal’) and L. peruvianum (P.I. 251306) were grown from seed in a phytotron at 26/18 C day/night temperature superimposed on a photoperiod of 9 hr of high-intensity light plus 1 hr of incandescent light. Three days before inoculation, plants were transferred to the different temperature regimes. Plants were inoculated by stabbing the stem above the cotyledonary leaves with a dental root-canal file dipped in a suspension containing 10⁷ cells/ml of Corynebacterium michiganense. “Resistance” in this paper refers to the resistance to infection when the pathogen is introduced directly into the vascular system. Differences in disease ratings between resistant and susceptible accessions were greater in 5-week-old plants (16-to 24-cm tall) than in 4-, 6-, and 7-week-old plants. The age × accession interaction was significant. Five-week-old plants at 24/18 C showed greater differences in disease ratings than those at 20/18, 28/18, or 32/18 C, and the temperature × accession interaction was significant. Inoculum that contained 10⁹ cells/ml induced larger differences in disease ratings in 5-week-old plants at 24/18 C than inoculum with 10⁵ and 10⁷ cells/ml, but inoculum with 10⁷ cells/ml induced differences almost as great as that with 10⁹ cells/ml.