Studies on the origin of crop species by restriction endonuclease analysis of organellar DNA. III. Chloroplast DNA variation and interspecific relationships in the genus Secale.

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Abstract
In order to obtain new information on interspecific relationships in the genus Secale, and the phylogenetic relation of Secale to two related genera, Triticum and Aegilops, a restriction endonuclease analysis of chloroplast (ct) DNAs isolated from five Secale species was conducted. First, ctDNA of S. cereale was analyzed using eight restriction endonucleases, and its physical map was constructed by referring to that of T. aestivum. Next, ctDNAs of all five Secale species were analyzed using three endonucleases, BamHI, PstI and SmaI. The chloroplast genome size of all the species was estimated to be about 136kbp, which is very close to those of Triticum and Aegilops. The ctDNA of all the species but S. silvestre produced identical restriction fragment patterns with all the enzymes employed, suggesting early separation of S. silvestre from the rest of species. The patterns of S. silvestre showed one to two fragment differences from those of the four other Secale species. The chloroplast genomes of S. cereale (and other species) and S. silvestre differed by at least three mutations and were designated S1 and S2, respectively. Both chloroplast genomes were closely related to those of Triticum and Aegilops. The magnitude of the chloroplast genome diversification in Secale was almost the same as in Triticum, Aegilops, Hordeum and Avena.