Source of Resistance to Black Rot of Cabbage Expressed in Seedlings and Adult Plants

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Abstract
About 350 accessions of cabbage (Brassica oleracea var. capitata) in the U. S. Plant Introduction Station collection were screened as seedlings for resistance to black rot by spraying a suspension of bacterial cells of Xanthomonas campestris pv. campestris onto leaves with guttation droplets in a greenhouse mist chamber. The bacterial cells were drawn into the leaves via the hydathodes when drying conditions were provided. Seedlings were inoculated 2.5 wk after sowing when the first true leaf was about 2.5 cm long. Several lines with excellent resistance as adult plants were highly susceptible under these conditions. However, PI 436606, an introduction from china, was resistant at this early stage as well as at later stages of maturity. The resistant introduction was challenged by 16 strains of X. c. pv. campestris that induced typical black rot symptoms, leaf blight, or symptoms intermediate between those of black rot and leaf blight on susceptible plants and was found effective against all strains. PI 436606 also was resistant against a closely related pathogen, X. c. pv. armoraciae, that induces leaf blight and hydathode necrosis symptoms on susceptible plants.