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

Abstract

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 BC2Rfo-positive individual 16CMSF2-11 and its BC3 progenies, with 18 chromosomes, were developed, which were morphologically identical to the parent Chinese kale. Compared with F1 and BC1 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 BC3Rfo-progenies recovered to the parent Chinese kale, while most or all of the An-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.

A Modified Meiotic Recombination in Brassica napus Largely Improves Its Breeding Efficiency

“…Even if these later CCA hybrids are more difficult to generate [76], improved recombination between homologous C chromosomes would also strongly benefit B. napus breeding programs. In fact, different studies revealed that it could be useful to introduce into B. napus new diversity from B. oleracea [77], such as clubroot resistance traits [78], and conversely from B. napus to B. oleracea [79]. It will also be interesting to determine if this modified homologous recombination landscape is also present in the other possible allotriploids from the U triangle [80], e.g., either AAB (deriving from B. juncea × B. rapa) or CCB (B. carinata × B. oleracea) hybrids, and thus possibly be useful for Brassica breeding.…”

Organelle Comparative Genome Analysis Reveals Novel Alloplasmic Male Sterility with orf112 in Brassica oleracea L.

“…In addition, previous studies have shown that Ogura CMS and Kos CMS have the same restorer gene (Rfo/Rfk) [62], so the fertility of Bel CMS is likely to be restored by this restorer gene. We have hybridized Bel CMS with a fertile line containing the Rfo gene [1,63], and the fertility was successfully recovered, which showed that all three kinds of CMS can be fertility-restored by the same Rfo gene.…”

“…capitata) is an important leafy vegetable crop that is widely cultivated worldwide. As a typical cross-pollinated plant, cabbage exhibits noticeable heterosis, and hybrids usually have better growth potential, yield, and disease resistance than their parents [1]. The utilization of heterosis in Brassica crops depends mainly on either self-incompatible or male-sterile lines [2].…”

“…CMS derived from interspecific or intergeneric hybridization and somatic cell fusion is often referred to as alloplasmic CMS [10]. The most widely used alloplasmic male-sterile line in B. oleracea is the Ogura CMS, which was introduced from radish [1]. Although the Ogura CMS line has greatly improved the seed purity of B. oleracea and has undergone several rounds of improvements [11,12], many undesirable traits affecting seed yield are still present, such as a high rate of withered buds, small nectaries, a light petal color, and low seed production.…”

Mechanism and Utilization of Ogura Cytoplasmic Male Sterility in Cruciferae Crops

“…The Rfo restorer gene was introduced from B. napus to B. oleracea by the bridge material Brassica alboglabra Bailey [ 80 , 81 , 82 ]. Using triploid and hexaploid methods, several Ogura CMS fertility-restored plants of B. alboglabra Bailey were successfully created.…”