Creation of fertility-restored materials for Ogura CMS in Brassica oleracea by introducing Rfo gene from Brassica napus via an allotriploid strategy

KEY MESSAGE: Ogura CMS fertility-restored materials, with 18 chromosomes, normal seed setting, stable fertility and closer genetic background to the parent Chinese kale, were successfully developed in B. oleracea via a triploid strategy for the first time. ABSTRACT: Ogura cytoplasmic male sterility (CMS) is the most widely used sterile type in seed production for commercial hybrids of Brassica oleracea vegetables. However, the natural Ogura CMS restorer line has not been found in B. oleracea crops. In this study, the triploid strategy was used with the aim to create euploid B. oleracea progenies with the Rfo gene. The allotriploid AAC hybrid YL2 was used as a male parent to backcross with Ogura CMS Chinese kale. After successive backcrosses, the BC(2) Rfo-positive individual 16CMSF2-11 and its BC(3) progenies, with 18 chromosomes, were developed, which were morphologically identical to the parent Chinese kale. Compared with F(1) and BC(1) plants, it showed stable fertility performance, and regular meiosis behavior and could produce seeds normally under natural pollination. The genomic composition analysis of Rfo-positive progenies by using molecular markers showed that more than 87% of the C-genome components of BC(3) Rfo-progenies recovered to the parent Chinese kale, while most or all of the A(n)-genome segments were lost in 16CMSF2-11 and its progenies. The results suggested that the genetic background of Rfo-positive individuals was closer to that of the parent Chinese kale along with backcrossing. Hereof, the Ogura CMS fertility-restored materials of Chinese kale were successfully created via triploid strategy for the first time, providing a bridge for utilizing the Ogura CMS B. oleracea germplasm in the future. Moreover, our study indicates that the triploid strategy is effective for transferring genes from B. napus into B. oleracea. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00122-020-03635-8) contains supplementary material, which is available to authorized users.