Introgression of Blackleg Resistance from Brassica Carinata into B. napus and Mapping the Resistance Genes.

Blackleg disease (caused by Leptosphaeria maculans) in canola (Brassica napus, AC genome, n = 19) result in significant yield losses. However, Ethiopian mustard (Brassica carinata, BC genome, n = 17), that carries the B genome, shows excellent resistance to this disease at both the cotyledon and adult plant stages. To introgress resistance from B. carinata into B. napus canola, crosses between B. napus cv. Westar and B. carinata were made, and the interspecific hybrids were backcrossed twice to Westar and self-pollinated three times with selection in each generation for cotyledon resistance to Leptosphaeria maculans PG2-type isolate. Doubled haploid (DH) lines were produced from four cotyledon resistant BC₂S₃ families. Two cotyledon resistant DH lines (DH Popl#3) derived from the BC₂S₃ family 02-17006 were crossed to the blackleg susceptible B. napus cv. Polo and two DH populations (Popl#3¹¹⁵¹ and Popl#3¹¹⁵²) were produced from the F₁’s. Similarly, a cotyledon resistant DH line (DH Popl#4) derived from the BC₂S₃ family 02-17009 was crossed to Westar and a DH population (Popl#4.1) was produced. Four resistant DH lines of the Popl#4 and two lines of Popl#4.1 were crossed to Polo and six DH populations, Popl#4¹⁰⁶⁸, Popl#4¹⁰⁶⁹, Popl#4¹⁰⁷⁰ and Popl#4¹⁰⁷¹, Popl#4.1¹¹⁵⁴ and Popl#4.1¹¹⁵⁵, were produced from the F₁’s. Simple sequence repeat (SSR) marker analysis and genomic in situ hybridization (GISH) was done to study the inheritance of resistance and map the resistance genes. The resistant DH lines of the populations Popl#3, Popl#3¹¹⁵¹ and Popl#3¹¹⁵² carried the B genome chromosome B3, and the resistance gene was located in the middle to bottom segment of this chromosome. In the case of the DH populations Popl#4.1, Popl#4¹⁰⁶⁸, Popl#4¹⁰⁶⁹, Popl#4¹⁰⁷⁰ and Popl#4¹⁰⁷¹, Popl#4.1¹¹⁵⁴ and Popl#4.1¹¹⁵⁵, cotyledon resistance followed a Mendelian segregation and a single SSR marker associated with this resistance was identified. Unlike the Popl#3 DH lines, no B genome chromosome was detected in these resistant DH lines. Whether the resistance gene in Popl#4 and Popl#4.1 introgressed from the B or C genome of B. carinata and pyramiding of this gene with the resistance gene of Popl#3 would exhibit resistance to more virulent L. maculans isolates at the cotyledon and adult plant stages needs to be investigated.