Inheritance of the resistance to Leptosphaeria maculans of Brassica nigra and B. juncea in near-isogenic lines of B. napus

The inheritance of resistance to Leptosphaeria maculans was studied in near-isogenic lines derived from asymmetric somatic hybrids between Brassica napus+Brassica nigra and Brassica napus+Brassica juncea, respectively. The hybrids had been backcrossed to B. napus for seven generations before the genetic segregation of the blackleg resistance was determined. The results of the inheritance studies suggested that one single dominant allele controls the resistance in the Brassica napojuncea line, whereas two independent dominant loci were found in the Brassica naponigra line. Total leaf DNA from the near-isogenic lines was isolated and 89 loci were detected by hybridization to 66 restriction fragment length polymorphism (RFLP) markers previously mapped in the B. nigra genome. Out of the 89 loci, eight loci were detected in the B. naponigra line and six were found in the B. napojuncea line. RFLP markers co-segregating with blackleg resistance in adult leaves were also found. Two markers associated with linkage group 5 and 8, respectively, of the B genome were found in the B. naponigra line and one marker was associated with linkage group 2 in the B. napojuncea line.