| Results and Discussion The number of the fertile and sterile plants, that were studied in the F2 hybrids between R-17127 and MS Aurora and MS Roussalka with the cytoplasms of T. timopheevi, T. dicoccoides var. spontaneovillosum and Ae. speltoides are presented in Table 1 together with the proposed segregation ratios. The results show that the male fertility restoration in the hybrids between R-17127 and the MS lines of Aurora is governed by one dominant gene. However, the segregation ratios between the fertile and the male sterile plants in the F2 generation of the cross between R-17127 and the MS lines of Roussalka correspond to 54:10. This result suggests that three Rf-genes function in these hybrids and the complementary action of at least two of them is necessary in order to achieve even slightly lower levels of male fertility in the MS lines of Roussalka in comparison to MS Aurora (ref. Table 2 in Panayotov et al. 1987). Common wheat cultivars differ in their ease of restoration, that is, significant variation has been reported in the level of the restored male fertility when MS lines of different cultivars were pollinated by the same R-line (Wilson 1976; Mihaljev 1976; Jost & Milohnich 1976; Gotsov 1981). In general, this phenomenon had been explained with the presence of weak fertility restoring genes in the genetic background of some wheat cultivars and their interaction with the Rf-genes of the restorer lines. The data from the monosomic analysis presented an additional evidence in proof of the complex genetic basis of male fertility restoration by R-17127 (Table 2). The segregation between the fertile and sterile plants in the disomic test-cross fitted a 15:1 ratio. Moreover, about seventy percent of the plants belonging to the fertile class showed self seed fertility above 75% (Fig. 1). This fact suggests that four dominant Rf-genes might be involved in the control of male fertility restoration by R-17127. Two of them are located on chromosomes 1A and 6B of R- 17127 because test-crosses with mono-1A and -6B showed significantly higher proportion of the fertile class in comparison to the disomic line. From previous studies (Yen et al. 1969; Bahl & Maan 1973) it is known that four genes, Rf1, Rf2, Rf4 and Rf5, all of which originate from T. timopheevi, are located on chromosomes 1A, 7D, 6B and 6D, respectively. R-17127 seems to possess two of them, i.e. Rf1 and Rf4, while its chromosome 5B may carry another Rf-gene. The present results also suggest that three Rf-genes are located on chromosomes 3A, 2B and 3D of Chinese Spring. Their interaction with the fertility restoring genes of R-17127 to give a 15:1 ratio in the disomic line must be a subject of future investigations. Conclusions Line R-17127 possesses a complex genetic system for male fertility restoration against the CMS-inducing cytoplasms of G plasma type. This system probably includes four Rf-genes, two of which were found to locate on chromosomes 1A and 6B. However, their penetrance and expressivity can be modified depending on the genetic background of the MS Iine. Further studies are necessary for the chromosomal location of the other two Rf-genes of R-17127 and for complete understanding of the interactions that determine the conditions for their full expression. Acknowledgement The authors wish to express their gratitude to Prof. K. Tsunewaki, Laboratory of Genetics, Kyoto University, Japan for critical reading of the manuscript and valuable suggestions. References BAHL, P. N. & S. S. MAAN. 1973. Chromosomal location of male-fertility restoring genes in six lines of common wheat. Crop Sci., vol. 13:317-320. GOTSOV, K. 1981. Present status and problems in hybrid wheat. (in Bulg.). Selskostopanska nauka XIX, 3:81-90. JOST, M. & J. MILOHNICH. 1976. Search for new sources of genes for pollen fertility restoration. Poljoprivredna snanstvena smotra 38(48):73-77. MIHALJEV, I. 1976. The influence of some factors on the fertility restoration in cytoplasmic male sterile wheat lines. Poljoprivredna snanstvena smotra. 38(48):79-84. PANAYOTOV, I., D. K. GOTSOVA & K. GOTSOV. 1987. Male fertility restoration agains various alien cytoplasms. I. Comparison between the restoration abilities of three groups of lines. Wheat Inf. Service. SEARS, E. R. 1954. The aneupoloids of common wheat. Res. Bull. Mo. Exp. Stat. 572. WILSON, J. A. 1968. Hybrid wheat development with Triticum timopheevi Zhuk. derivatives. Proc. 3rd Int. Wheat Genet. Symp., Canberra:423-430. YEN, F. S., L. E. EVANS & E. N. LARTER. 1969. Monosomic analysis of fertility restoration in three restorer lines of wheat. Can. J. Genet. Cytol., 11:531-546. |
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