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Genetics

Development of Monogenic Lines for Resistance to Albugo candida from a Canadian Brassica napus Cultivar. J. Q. Liu, Department of Plant Science, University of Manitoba, Winnipeg, MB, Canada, Current address: Agriculture and Agri-Food Canada, Cereal Research Centre, 195 Dafoe Road, Winnipeg, MB; P. Parks, and S. R. Rimmer. Department of Plant Science, University of Manitoba, Winnipeg, MB, Canada. Phytopathology 86:1000-1004. Accepted for publication 28 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-1000.

Resistance to Albugo candida race 7 in the Canadian Brassica napus cultivar Regent is conditioned by three dominant genes, designated Ac7₁, Ac7₂, and Ac7₃. Gene Ac7₃ is present in a heterozygous condition. Homozygous resistant BC₁F₃ lines carrying Ac7₁ or Ac7₂ were developed from a BC₁F₁family in which segregation for white rust resistance fitted a 3 resistant (R):1 susceptible (S) ratio. To isolate the resistance genes, one BC₁F₃ line was assumed to have genotype Ac7₁Ac7₁ac7₂ac7₂ and was used as a tested to cross with other selected BC₁F₃ lines. Progenies from test crosses were self-pollinated and backcrossed to susceptible line 2282-9. Thus, two monogenic lines possessing Ac7₁ or Ac7₂ were developed as F₂ and backcross populations produced from four test crosses segregated to fit 15 R:1 S and 3 R:1 S ratios, respectively, whereas the other four lines were homozygous resistant. The two single-gene lines were used as testers to develop a monogenic line with Ac7₃ from a BC₁F₁ family that segregated in a 7 R:1 S ratio. These single genes are being incorporated into rapid-cycling B. napus lines susceptible to several pathotypes of A. candida to develop isogenic differential lines. The monogenic lines will be used to study the mechanism(s) of resistance response conditioned by the individual genes. These lines also should facilitate molecular mapping of the loci in B. napus for resistance to A. candida race 7.