| Results and Discussion The following 20 common wheat cultivars or advanced true-bred lines were tested for presence of fertility-restoring genes against various alien cytoplasms, namely, Zlatna dolina, Vratsa, Charodeika, Skitiya, Preslav, Jubilei, Kaloyan, Zenith, Pliska, Zlatoklas, Trakiya, Bezostaya 1, Kubrat, Kiten, 780-124, 19-16-98, 76-76, 609-144, 203-206 and 13 A-305. In the majority of the cases the F1 hybrids between these cultivars and the MS lines with the cytoplasms of Ae. triuncialis, Ae. mutica, Ae. comosa, Ae. speltoides, T. dicoccoides var. spontaneovillosum and T. timopheevi were completely sterile ; the low levels of selfed seed fertility (between 0.2 and 4.6%), observed in some of the hybrids were most probably due to failure in timely bagging. It is clear that the frequency of Rf-genes against the tested CMS-sources is very low, at least among the Bulgarian-bred common wheat cultivars and as such they should be regarded as maintainers of sterility. The first group of fertility restorers tested in the present study comprised of the ten R-lines listed in Table 1. They were selected as fertile plants in the course of the backcross procedure used for the production of the alloplasmic lines and subsequently selfed to obtain the Rf-gene(s) in homozygous condition. The selfed seed fertilities of the F1 hybrids between this group of restorers and the MS lines are also given in Table 1. It might be pointed out that, with two exceptions, these R-lines are ineffective or possess very weak male fertility-restoring genes against the cytoplasms of Ae. triuncialis, Ae. mutica, Ae. comosa, Ae. speltoides, T. dicoccoides var. spontaneovillosum and T. timopheevi. The lines R-17 and R-56 restored moderate levels of male fertility (51.4 and 55.2%, respectively) in their hybrids with male sterile wheat with Ae. triuncialis and Ae. mutica cytoplasms. Male fertility-restoring genes against the cytoplasm of Ae. triuncialis could be found in a number of diverse sources, e.g. not only in Ae. recta (R-17), but also in Ae. caudata (R-9) and T. monococcum (R-68), as well as in Ae. triuncialis (R-5) itself. The cytoplasm of Ae. triuncialis, available at the Institute for Wheat and Sunflower derives its origin from Ae. caudata (MUKAI et al. 1978) and it was assigned by Tsunewaki (1980) to the same plasma type (C) as its donor. It is quite natural then, that the species, donor of the sterile cytoplasm, harbors male fertility-restoring genes against that same cytoplasm. The second group of R-lines consisted of R-17127, R-3206-143 and R-3169-5. They were produced by the breeding method, which is usually employed for the production of common wheat cultivars , but the whole procedure is carried out on the basis of T. timopheevi cytoplasm. As a consequence, these R-lines manifest high selfed seed fertility, short stem, strong disease resistance and very good grain quality. The levels of male fertility-restoration in the F1 hybrids between R-17127, R-3206-143 and R-3169-5 and the MS lines, included in the present investigation, are given in Table 2. Although the results differ between hybrids, it is clear that the R-lines show the highest efficiency against the cytoplasm of T. timopheevi. The level of male fertility restoration in the cross-combination MS (timopheevi)-Aurora x R-17127 (90.8%) is even higher than the selfed seed fertility of euplasmic Aurora. The other two R-lines are slightly less effective against the cytoplasm of T.timopheevi, when compared with R-17127. |
| <-- Back | | | --> Next |