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Selection for Minor Gene Resistance to Albugo candida in a Rapid-Cycling Population of Brassica campestris. M. D. Edwards, Department of Horticulture, University of Wisconsin, Madison 53706, Present address: Genetics Department, North Carolina State University, Raleigh 27695-7614; P. H. Williams, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 77:527-532. Accepted for publication 30 June 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-527.

Three cycles of selection for resistance to Albugo candida race 2 were conducted within a rapid-cycling population of Brassica campestris that was devoid of major resistance genes. Both mass selection and selection between and within half-sib families were effective in accumulating minor genes conferring reduced pathogen sporulation. Sporulation ratings declined linearly from 4.2 in cycle 0 to 1.3 in cycle 3 of half-sib family selection and 0.95 in cycle 3 of mass selection. Evaluation of testcross generations from cycle 3 resistant cycle 0 susceptible crosses failed to discriminate segregation of individual factors contributing to the accumulated resistance. Estimates of gene number and the degree of dominance were demonstrated to be dramatically influenced by changes in scaling of the sporulation ratings used.

Additional keywords: polygenic resistance, quantitative resistance, response to selection.