Development and characterization of a complete set of monosomic alien addition lines from Raphanus sativus in Brassica oleracea.

Key message: A complete set of monosomic alien addition lines of Radish-Brassica oleracea exhibiting extensive variations was generated and well characterized for their chromosome behaviors and phenotypic characteristics. Monosomic alien addition lines (MAALs) are developed through interspecific hybridization, where an alien chromosome from a relative species is introduced into the genome of the recipient plant, serving as valuable genetic resources. In this study, an allotetraploid Raphanobrassica (RRCC, 2n = 36) was created from the interspecific hybridization between radish (Raphanus sativus, RR, 2n = 18) and Brassica oleracea (CC, 2n = 18). Subsequently, this Raphanobrassica was repeatedly backcrossed with radish to generate an aneuploid population. The identification of a complete set of MAALs (RR + 1C_1-9, 2n = 19) was achieved using PCR with C chromosome-specific markers and fluorescence in situ hybridization, revealing extensive morphological variations, particularly in the shape and size of the fleshy root. A complete set of MAALs was achieved with only one chromosome from 1 to 9 linkage groups of the C genome. Compared with parental radish, most of the MAALs showed a noticeable delay in root swelling, particularly the RR-C₆ that did not exhibit obvious root swelling throughout its entire growth stage. Cytological analysis indicated that the MAAL lines containing chromosome C₈ exhibited the highest frequency of intergenomic chromosome pairings. Additionally, some introgressive radish lines derived from MAALs displayed a preference toward the donor B. oleracea or over-parent heterosis for some certain nutritional components. Overall, these MAALs serve as valuable germplasm for the genetic enhancement of radish and provide insights into the interactions between the R genome and C chromosomes.