| Results and Discussions The fertilities observed at Step 3 are shown in Table 1. There were 13 chlorotic plants in addition to 23 normal plants classified as sterile (four) and as fertile (19). This gregation fits 1:3 ratio (X2=0.710, d.f.=1) but not 1 : 1 ratio (X2=9.783, d.f.=1), suggesting that T. macha carries two dominant Rf genes against the timopheevi cytoplasm. In order to verify two gene control system, four fertile plants obtained were selfed to examine their progenies on the segregation pattern of fertilities. The results are summarized in Table 2. Three of the four lines (#1, #3 and #4) satisfactorily fit 1 (sterile): 3 (fertile) ratio (X2=0.029. 0.017 and 1.127, respectively), suggesting that the parents of these lines had only one of the two Rf genes of T. macha. On the other hand, line #2 significantly deviated from 1 : 3 ratio (X2=5.839), but rather fitted 1 : 15 ratio (X2=3.007). Therefore, the parent of line #2 might have received both of the Rf genes of T. macha. In the present experiment, lines #1, #3 and #4 as well as #2 showed similar range of selfed seed fertility. The plant which showed the highest fertility in line #2 was selfed and backcrossed to Chinese Spring to test the restoration ability of the Rf gene. The results obtained in the F3 and B1F1 generations are shown in Table 3. It is clearly demonstrated that line #2-S1 (F3) is homozygous for the Rf genes, and most of them showed higher than 80% of selfed seed fertility. While, the B1F1 plants showed wide range in selfed seed fertility similar to those in F2 (about 20 to 90%). MILLER et al. (1974) reported that a common wheat cultivar Primepi has two fertility-restoring genes against timopheevi cytoplasm, and complete fertility restoration was ensured when both genes were present, either in the homozygous or heterozygous condition. The heterozygote or homozygote alone of either of the two genes was incompletely fertile. The data in the present experiment showed that the single Rf gene from T. macha can restore almost complete fertility in homozygous state and also in some of the heterozygotes. In other heterozygotes, however, the Rf gene showed instability in fertility. This may be partly due to the gene interaction between Rf gene and background genes. FUJIGAKI and TSUNEWAKI (1976) reported that the timopheevi cytoplasm increased the inter-plant variation on four growth characters of common wheat. Therefore, the variation found on selfed seed fertility may be partly due to the increased developmental instability caused by the timopheevi cytoplasm. In this study, Rf genes were transfered into a common wheat cultivar from T. macha. However, instability of gene expression of Rf gene in heterozygous condition is a problem which should be resolved either through an appropriate combination of Rf genes or in breeding an easy restoration background. |
| <-- Back | | | --> Next |