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Nucleus substitution lines with Ae. ovata cytoplasm Male-steriles: In all the 11 varieties pollen fertilities (percentage of good pollen grains) and selfed seed fertilities (estimated from the seed set in the first and second florets) in F1 and the following backcross generations were checked. All the varieties exhibited complete absence of good pollen and no seed fertility (0.0%) in the F1 as well as in the subsequent backcross generations, with the exception of Pak Kohni. In this particular strain of T. sphaerococcum, out of 13 plants of the first substitution-backcross generation (SB1) two plants exhibited partial pollen (31.7%) and seed fertilities (8.3%). The selfed seeds from those two plants were sown to check restoring genes, and again out of 21 plants, three plants showed partial seed fertility (6.5%). All the varieties of T. aestivum do not carry any restorer genes for Ae. ovata cytoplasm and complete sterility was induced. Fertility-restorer lines: To develop the counterpart restorer lines for the male-steriles, all the varieties were crossed to (ovata)-P168, an established restorer line of P168 having Ae. ovata cytoplasm. Their F3 hybrids exhibited varying degrees of pollen and seed fertilities, with the exception of Mexi-Pak 65 which showed complete male sterility in the F1 and also in the backcross generations (Table 1). Varieties C273, C591, Pak Kohni, AU49 and AU44 exhibited fairly high fertilities in all the generations, whereas in variety C271 the fertilities went on diminishing with the advancement of nucleus substitution, exhibiting 11.2% pollen and 0.0% selfed seed fertilities in SB3. Varieties C228 and Dirk became completely sterile from SB1 generation onward; H-68 also showed very low fertilities in F1 and SB1 generations. Complete lack of fertility in Mexi-Pak 65. C228 and Dirk indicates that the restorer gene(s) of P168 does not restore fertility in these varieties in heterozyhgous condition. It will be necessary to seek new sources of restoring genes for those varieties. Nucleus substitution lines with T. timopheevi cytoplasm Male-sterile lines : Estimation of pollen and selfed seed fertilities in the F1 and subsequent backcross generations revealed that none of the 11 varieties carry effective restoring genes, as all the lines became completely male sterile in the advanced backcross generations (Table 2). Fertility-restoration lines : All the varieties exhibited very high pollen as well as selfed seed fertility in the F1 generation (timopheevi- T. spelta duhamelianum x Pakistani varieties), indicating the strong fertility-restoring capability of spelta's restorer gene, Rf3, for T. timopheevi cytoplasm (Table 2). Varieties Mexi-Pak 65 and Dirk exhibited complete sterility in their backcross generations ; whereas the rest of the varieties showed fairly high fertilities even in their most advanced backcross generations. (Received September 8, 1969) |
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