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

Abstract

Cytoplasmic male sterility (CMS) is the most commonly used mechanisms for developing F1 hybrids in Brassica oleracea. Ogura cytoplasm is the only source of CMS system used widely in B. oleracea and diversification of CMS system is needed to avoid any imminent epidemic. We have developed sesquidiploids and backcross progenies involving the cybrid, B. napus with B. tournefortii (Tour) cytoplasm and B. oleracea for development of novel CMS system through different approaches of in vitro embryo rescue. Maturity of the ovaries and ovules were found to play important role in recovery of inter-specific hybrids through embryo rescue. The male sterility conferred by ‘Tour’ cytoplasm was partially restored by Rf genes in the B. oleracea nuclear genome and identification of perfect maintainer is necessary in developing ‘Tour’ based CMS system. The analysis of the sesquidiploid F1 hybrids and back-cross progenies revealed frequent occurrence of A and C sub-genome aneuploids and euploids. Chromosome elimination and fragmentation of the A and C genome specific linkage groups indicated the role of autosysndesis and allosyndesis in the AnCnCo sesquidiploid. The dominance of the B. napus like gametes was also evident in the first backcross progenies. The developed back-cross population with ‘Tour’ cytoplasm will be useful in developing stable CMS system in B. oleracea as an alternative to the available Ogura based lines for commercial hybrid breeding programme.