Back-cross introgression of ‘Tour’ cytoplasm from Brassica napus through in vitro embryo rescue reveals partial restoration of sterility in B. oleracea

•Introgression of Brassica tournefortii male sterile cytoplasm into B. oleracea through in vitro embryo rescue.•Direct embryo culture protocol for successful inter-specific hybridization between B. napus × B. oleracea.•Established presence of Rf genes or poor stability of ‘Tour’ cytoplasm in B. oleracea nuclear background.•Abnormal meiotic behaviour in the back-cross progenies detected through A and C genome specific uniquely mapped SSRs.