Molecular and biological studies on male-sterile cytoplasm in the Cruciferae. III. Distribution of Ogura-type cytoplasm among Japanese wild radishes and Asian radish cultivars.

The distribution of Ogura male-sterile cytoplasm among Japanese wild radish populations and Asian cultivated radishes was studied by means of polymerase chain reaction (PCR)-aided assays using mitochondrial atp6 and orf138 loci as molecular markers. Three separate PCR experiments were performed to amplify the target sequences in normal-type atp6, Ogura-type atp6, and Ogura-specific orf138, and the cytoplasm of each plant was classified as either normal or Ogura. Among 217 wild radish plants, 93 had both Ogura-type atp6 and orf138 (or its modified form), whereas 124 had normal-type atp6. Of the 93 plants with Ogura-type cytoplasm, only a single plant showed male sterility. A complete linkage between Ogura-type atp6 and orf138 loci was found in Japanese wild radishes, confirming our findings that Ogura-type cytoplasm is distributed widely among Japanese wild radish populations. A modified form of orf138 (orf138-S) was identified in a few wild radish populations in a limited area of Japan, and the nucleotide sequence of the orf138-S revealed a 39-bp deletion shared in common with 'Kosena' male-sterile cytoplasm. Among the 44 Asian cultivars analyzed, 40 were determined to have normal cytoplasm since all 4 plants tested in each cultivar showed the same PCR amplification profiles as that of 'Uchiki-Gensuke', a reference cultivar with normal cytoplasm. The plants with Ogura-type cytoplasm (or its modified form) were found in 1, 1, and 2 cultivars from Tibet, Japan, and Taiwan, respectively. Except for 1 cultivar from Taiwan, those with Ogura-type cytoplasm included a few plants having male sterility. The multiple and independent introduction of Ogura-type cytoplasm from the wild radish in Asia into these cultivars is suggested.