DEVELOPMENT OF MONOGENIC LINES FOR RESISTANCE TO ALBUGO-CANDIDA FROM A CANADIAN BRASSICA-NAPUS CULTIVAR

Resistance to Albugo candida race 7 in the Canadian Brassica napus cul tivar Regent is conditioned by three dominant genes, designated Ac7(1) , Ac7(2), and Ac7(3). Gene Ac7(3) is present in a heterozygous conditi on. Homozygous resistant BC1F3 lines carrying Ac7(1) or Ac7(2) were de veloped from a BC1F1 family in which segregation for white rust resist ance fitted a 3 resistant (R):1 susceptible (S) ratio. To isolate the resistance genes, one BC1F3 line was assumed to have genotype Ac7(1)Ac 7(1)ac7(2)ac7(2) and was used as a tester to cross with other selected BC1F3 lines. Progenies from test crosses were self-pollinated and bac kcrossed to susceptible line 2282-9. Thus, two monogenic lines possess ing Ac7(1) or Ac7(2) were developed as F-2 and backcross populations p roduced 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 res istant. The two single-gene lines were used as testers to develop a mo nogenic line with Ac7(3) from a BC1F1 family that segregated in a 7 R: 1 S ratio. These single genes are being incorporated into rapid-cyclin g B. napus lines susceptible to several pathotypes of A. candida to de velop isogenic differential lines. The monogenic lines will be used to study the mechanism(s) of resistance response conditioned by the indi vidual genes. These lines also should facilitate molecular mapping of the loci in B. napus for resistance to A. candida race 7.