2024 Volume 26 Issue 2 Pages 113-123
The Japanese radish (Raphanus sativus L.) native variety ‘Akka’, with red root skin, is a fixed variety. In addition to the basic red color, individuals with red neck and white skin sometimes occur. In this study, we focused on the anthocyanin coloring gene of ‘Akka’ and elucidated the mode of inheritance through crossing tests. We investigated the segregation ratio of inbred progeny, test cross results, and the F2 generation using the fixed lines in ‘Akka’. Root skin pigmentation was well adapted to the inheritance of dominant epistasis involving two dominant genes: red (R1--), red neck (r1r1R2-), and white (r1r1r2r2). The dominant R1 gene, which causes the entire root skin to be colored red by anthocyanins, is epistatic to the R2 gene, which expresses the red neck, and was expressed regardless of the presence or absence of the R2 gene. The R2 gene is dominant and causes anthocyanin-induced red neck expression only in the absence of R1 gene. When both genes are absent, the roots do not show anthocyanin coloration, and appear white. The linkage groups on which the R genes are located were deduced from the results of crossing ‘Akka’ with other colored root cultivars, test cross results, and prior findings. The R1 gene is part of the linkage group Rs7 which is the same as the Chinese cultivar ‘Koshin’ (Chinese name ‘Xinlimei’), while the R2 gene is part of the linkage group Rs2 which is the same as the Western small radish cultivar ‘Comet’. Root skin color did not differ between individuals with heterozygous and homozygous R1 genotypes. However, in flower stems, petals, and pods, anthocyanins were more likely to be expressed in heterozygous than in homozygous conditions. Individuals with reddish petals and red pods were mostly heterozygous for R1 gene. Based on these findings, selecting individuals with less anthocyanin in flower stems, petals, and pods is thought to lead to immobilization of the R1 gene.
