| Transfer of the fertility-restoring genes of Triticum
macha into a common wheat cultivar Junzo FUJIGAKI Laboratory of Genetics and Plant Breeding, Junior College, Tokyo University of Agriculture, Tokyo 156, Japan Large scale cultivation of hybrid wheats is not yet established apart from maize, sorghum and other crops 20 years after the discovery of cytoplasmic male sterility (KIHARA, 1951), although small scale cultivations are done at some limited areas in U.S.A., using the seeds commercially released by a few seed companies. This is mainly due to the difficulties to breed restorer lines which makes the respective hybrids to show stable fertilites under various climatic conditions. Therefore, the most important aim in the present program of hybrid wheat breeding is to obtain Rf genes having stable and strong fertility restoration ability. KIHARA and TSUNEWAKI (1966) reported that Triticum macha var. subletschchumicum has a fertility restoring gene(s) to timopheevi cytoplasm, which could be utilized in hybrid wheat program. However, T. macha has a hybrid chlorosis gene Ch1 on chromosome 2A (Hermsen and Waninge 1972, Tsunewaki 1975), while most of common wheat cultivars have Ch2 on chromosome 3D (TSUNEWAKI and KIHARA 1961). Therefore, it is difficult to transfer a restorer gene(s) directly from T. macha to common wheat through crossing due to the hybrid chlorosis caused by the complementary gene action between the Ch1 and Ch2. Accordingly, T.macha has not yet been utilized as a source of restorer gene. The present experiment was aimed to transfer fertility-restoring gene from T. macha to a common wheat cultivar by a bridging cross. Materials and Methods A procedure illustrated in Fig. 1, assuming that a single dominant gene (Rf) restores fertility, was adopted for the transfer of the Rf gene of Triticum macha to a common wheat. A strain, NIG-2 (by TSUNEWAKI 1975) free from both the complementary chlorosis genes, was employed as the bridging parent in the present investigation. NIG-2 was first employcd as the female parent in a cross with T. macha var. subletschchumicum (abbreviated as T. macha). The F1 plants at Step 1 (Fig. 1) should therefore have Rf and Ch1 in heterozygous condition. To separate Rf from Ch1, the F1 plants were used as the male parents in the crosses with Chinese Spring having timopheevi cytoplasm (abbrevaited as (timopheevi)-CS), which has all rf, ch1 and Ch2 genes in homozygous state. Highly fertile segregants selected at Step 3 (Fig. 1) were selfed and their progenies were examined to determine the number of Rf gene involved. At the same time, those fertile plants were crossed with other Japanese cultivars as the secondary donors of the restorer gene(s). Selfed seed fertility of each individual was estimated from two ears covered with parafin paper bag in green house. The plants of selfed seed fertilities lower than 20% were classified as sterile, and those higher than 21 % as fertile. |
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