Evaluation of the propensity of interspecific hybridization between oilseed rape (Brassica napus L.) to wild-growing black mustard (Brassica nigra L.) displaying mixoploidy

•Significant interspecific hybridization in B. nigra (♀) x B. napus (♂) F1 hybrids.•Gene transfer evident in F1 hybrids under both controlled and open-field conditions.•Mixoploidy in wild-growing B. nigra increases hybridization propensity with B. napus.•Has gene flow from B. napus x B. nigra been underestimated in the environment so far?