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Bacterial Blight of Carrots: Interaction of Temperature, Light, and Inoculation Procedures on Disease Development of Various Carrot Cultivars. F. L. Pfleger, Research Plant Pathologist, ARS, USDA, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; G. E. Harman(2), and G. A. Marx(3). (2)(3)Assistant Professor of Seed Microbiology, and Professor, Department of Vegetable Crops, respectively, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 64:746-749. Accepted for publication 26 December 1973. DOI: 10.1094/Phyto-64-746.

High temp and high light intensity favored foliar symptom expression in carrot (Daucus carota L. var. sativa DC.) cultivars inoculated with Xanthomonas carotae (Kendr.) Dows. Photoperiod had little or no effect. As a group, ‘Danvers’, ‘Waltham HiColor’, and P.I. 306588 expressed greater tolerance to leaf blight than did ‘Spartan Sweet’, ‘Spartan Bonus’, and a susceptible breeding line (2106). When leaf tips were inoculated, the pathogen and lesions were confined to the area of inoculation. Although foliar symptoms were less severe at 20 C than at 25 C or 30 C, there was no corresponding reduction in the number of bacterial cells recovered from the affected tissue. When roots were wounded and immersed in suspensions of X. carotae, the bacteria caused extensive damage to the vascular system, much more at 30 C than at 20 C. In all tests, inoculation with the pathogen caused injury to tops and roots, expressed as a reduction in dry weight.

Additional keywords: Daucus carota, Xanthomonas carotae.