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A proposal for the designation of nucleus-substitution
lines and fertility-restoring genes in wheat K. TSUNEWAKI Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Kyoto, Japan Since the discovery of cytoplasmic male sterility of wheat caused byAegilops caudata cytoplasm (KIHARA 1951), a large number of alien cytoplasms have been successfully transferred to emmer and/or common wheat, most of them being found to induce male sterility. Their list is given in Table 1. In many institutions, nucleus-substitution work to introduce nuclei of various wheat cultivars into those cytoplasms is extensively carried out. Along with this, number of fertility-restoring genes, which have been factorially analyzed and located on specific chromosomes, is rapidly increasing. It seems, therefore, urgently needed to establish common rules for the designation of nucleus-substitution lines as well as fertilityrestoring genes : I will propose here the following rules for their designation. Designation of nucleus-substitution lines Rule 1. Name of the cytoplasm donor in italics to be shown in parantheses. Rule 2. Name of nucleus donor is given after the name of the cytoplasm donor, with a hypen between them. Example: (timopheevi)-Bison indicates a nucleus-substitution line of Triticum aestivum cv. Bison with the cytoplasm of T. timopheevi. Rule 3. The number of crosses made with the backcross parent is indicated, if necessary, by a superscript to the name of the nucleus donor. Example: (ovata)-Norin 2615 indicates the 14th backcross generation of T. aestivum cv. Norin 26 with the cytoplasm of Ae. ovata. Designation of fertility-restoring genes Rule 4. As the common, basic symbol, Rf meaning restored fertility, to be used. Rule 5. A third letter indicating the name of the cytoplasm, in which the designated gene functions as a restorer, is added after the common symbol. Example: A restoring gene to Ae. caudata cytoplasm is designated by Rfc. As already pointed out by KIHARA and TSUNEWAKI (1967), the function of a fertility-restoring gene is, in general, specific to a certain cytoplasm, and an effective gene for one cytoplasm does not necessarily function in other cytoplasms, unless they are related. Therefore, in designating the restoring gene, the name of cytoplasm, in which the gene functions, must be indicated. However, we should retain the symbol, Rf, for restoring genes in T. timopheevi cytoplasm, because three restoring genes for it have been already designated by this symbol (LIVERS 1964, TAHIR and TSUNEWAKI 1969). Rule 6. Non-allelic genes to the same cytoplasm are distinguished from each other by Arabic numerals given as subscripts to the symbol. Serial numbers starting from 1 should be given in the order of discovery. Example : Non-allelic, restoring genes to T. timopheevi cytoplasm are designated by Rf1, Rf2, Rf3, and so forth, in the order of discovery. Rule 7. When the same gene functions as a restorer to more than one cytoplasm, the symbol first given is retained. Applying these rules, the known restoring genes on a factorial basis will be designated as shown in Table 2. (Received October 1, 1969) |