Complete resistance to Leptosphaeria maculans, the cause of blackleg of oilseed rape (Brassica napus), was transferred from B. juncea to B. napus through an interspecific cross. B. juncea-type complete resistance (JR) was recognized first in one F3 progeny (OnapJR) by the absence of leaf-lesions on seedlings and canker-free adult plants. The commercially important characters of B. napus were retained in advanced lines of OnapJR, which combined JR with low erucic acid levels (<0.5%), high seed yield and variable maturity dates.
JR appeared to be inherited as a major gene or genes. Segregation for resistance and susceptibility contintied to occur during later generations of selection of OnapJR. JR was readily transferred from OnapJR to other suitable B. napus cultivars or lines with partial resistance to blackleg and resulted in highly vigorous carly generation selections adapted to cold, wet situations along with complete resistance to blackleg.