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Inheritance of Resistance in Cabbage to Black Rot. P. H. Williams, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; T. Staub(2), and J. C. Sutton(3). (2)Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; and (3)Assistant Professor, Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada. Phytopathology 62:247-252. Accepted for publication 8 September 1971. DOI: 10.1094/Phyto-62-247.

The Japanese cabbage cultivar, Early Fuji, known to have a high level of black rot resistance, was used as the source of resistance. Resistant lines were crossed to different susceptible inbred lines, and F₁, F₂, and backcross populations were screened during artificial black rot epidemics in the field. The only symptoms on resistant plants were necrotic hydathodes or necrotic marginal interveinal lesions, whereas the lesions on susceptible plants were v-shaped and surrounded by an expanding chlorotic zone. Black rot resistance was found to be controlled by one major gene, f, the expression of which in the heterozygous condition was influenced by one recessive and one dominant modifier gene. Of 300 cultivars and inbred cabbage lines screened for resistance to Xanthomonas campestris, none contained the major f gene for resistance found in Early Fuji. Among the 300 lines, reactions to X. campestris ranged from a highly tolerant lesion type with small, slowly spreading chlorotic margins, to those with highly susceptible systemic necrosis. Black rot reactions were classified from 1 to 5 in order of disease severity. All F₁ hybrid cultivars produced in the USA were highly susceptible to X. campestris; however, a number of Japanese hybrids were tolerant. Among a number of open-pollinated cultivars grown in the USA, particularly the ballhead types, individual plants showed high tolerance to black rot.