Characterization of Ogura CMS fertility-restored interspecific hybrids and backcross progenies from crosses between broccoli and rapeseed

Interspecific F1 hybrids were obtained from crosses between two Ogura cytoplasmic male sterility (Ogura CMS) broccoli lines (B14 and 137) and a rapeseed restorer line to introgress the Ogura CMS’s fertility-restoration gene Rfo from rapeseed into broccoli. Ten Rfo-positive interspecific, triploid plant progenies, phenotypically between rapeseed and broccoli, were obtained but still contained multiple rapeseed genes, with reduced fertility and seed setting potential under natural pollination. For fertility and seed setting improvement, successive backcrosses with broccoli were carried out to yield BC2 progenies. Screening revealed six plants with Rfo among 25 BC2 progenies, which were investigated for agronomic traits, ploidy determination, pollen viability and SSR (simple sequence repeat) markers to evaluate for ideal individuals closer to broccoli. Pollen viability tests were carried out at different stages for various hybrid parents. The results were as follows: 137-F1 (68.54%) > B14-F1 (65.32%) > 137-BC1 (48.15%) > B14-BC1 (32.41%). Although there were significant differences among the BC1 and BC2 individuals, the genetic background of BC2 was closer to the parent broccoli compared with that of BC1 plants. The existence of the Rfo gene in broccoli not only facilitates broccoli germplasm innovation, combination of interspecific hybridization and backcrossing, but may also shed light on trait segregation in different generations.