The distribution of the fertility restorer genes for Ogura cytoplasmic male sterility in Raphanus raphanistrum, Japanese wild radish, and cultivated radishes (R. sativus) was studied by observing the pollen fertility of the F₁'s from crosses with a male sterile strain having the Ogura cytoplasm. The restorer gene is widely distributed in the wild species and wild radishes irrespective of cytoplasm type. Among the cultivated radishes, the European and Chinese varieties had the restorer gene, while most of the Japanese cultivars did not.
The allelism of three restorer genes from R. raphanistrum, Japanese wild radish, and the European cultivar was estimated by the segregation of the fertility in the progenies produced by crosses between strains with different restorer genes. The results suggested that the restorer genes from these three sources were allelic.