Chromosome linkage study of Rf locus for cms-C
--Shaojiang Chen and Weicheng Chen

Restoration of the cms-C group of cytoplasms has been shown to be controlled by three complementary loci, designated Rf4, Rf5 and Rf6 (MNL 66:140, 1992). Rf4 has been located on the long arm of chromosome 8 (Sisco, Crop Sci. 31:1263, 1991); the location of Rf5 and Rf6 is unknown. No studies have been performed on the location of the Rf loci from China, though studies have shown that the restoration of cms-C is controlled by at least two loci (Chen, Acta Agron. Sin. 5:21-28, 1979). For this reason, it was hoped in this study that the restoring locus could be mapped and compared with the results above.

A series of crosses were made using two different cms-C fertile lines (Guang10-2, Jixi21), which had been confirmed to have one Rf gene, and a series of wx-translocation stocks which had been converted to cms-C sterility by crossing onto two different sterile lines (cms-ELB73 and cms-Ernan24).
The method used in our study was the same as Alice Johnson's (Johnson, MNL 58:102-103, 1984). The expected ratio was 3:1 (fertile:sterile).

Any cross exhibiting significantly > 25% sterility might be indicative of linkage of the Rf gene to the particular translocation since the wx T stocks were rf rf.

Tables 1-2 and Tables 3-4 were the results of two restoring lines on the sterile backgrounds cms-ELB73 and cms-Ernan24, respectively. Two crosses in Table 1 (No. 3, 4), one in Table 2 (No. 1), one in Table 3 (No. 5) and one in Table 4 (No. 12) exhibited a higher degree of fertility than expected, which could be explained by misclassification. The following crosses in the tables exhibited a much higher degree of sterility than expected: Table 1: T4-9b, T7-9a, T8-9d; Table 2: T6-9a, T7-9a; Table 3: T5-9a, T7-9a, T8-9d; Table 4: T7-9a.

It was very clear that the translocation, which couldn't be explained by misclassification or small size, was T7-9a. Therefore, the Rf locus for cms-ELB73 and cms-Ernan24 was the same one, and is on chromosome 7 near the breakpoint of T7-9a (7L.63, 9S.07). This showed a difference from the studies before. It seems reasonable to name it Rf5.

Table 1. Fertility for crosses Guang 10-2/translocations on the background of cms-ELB73.

Table 2. Fertility for crosses of Jixi21/translocations on the background of cms-ELB73.

Table 3. Fertility for crosses of Guang10-2/translocations on the background of cms-Ernan24.

Table 4. Fertility of crosses of Jixi21/translocations on the background of cms-Ernan24.

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