CMS-D8 restoration in cotton is conditioned by one dominant gene

Cytoplasmic male sterile (CMS-D8) and fertile restorer lines (D8R) of cotto n (Gossypium hirsutum L.) (AD(1)) were developed by transferring the cytopl asm and nuclear gene(s) from G. trilobum (DC.) Skovst. (D-8) into the cotto n nuclear background; Understanding the genetics of fertility restoration i n this CMS system is essential for its use in a hybrid breeding system. The objective of this investigation was to determine the mode of inheritance o f D8R restoration to CMS-D8. The experimental approach involved a series of crossing schemes involving nuclear permutations among the AD(1) and D-8 al loplasms. Eighteen normal genotypes did not restore fertility to the CMS-DS (A line) and could be used as maintainer (B) lines. D8R crossed as female with B lines yielded F-1 and F-2 populations with all fertile plants. F-1 p ollen also produced all fertile progeny in crosses on A lines. Thus, the D- 8 restorer functions at the gametophytic level. When heterozygous restored plants were pollinated with B lines, or when reciprocal F-1's with normal c ytoplasm,were crossed as male with the A line, the progeny ratio was one fe rtile to one sterile. A 3:1 ratio was obtained when restored F-1 plants wit h D-8 cytoplasm were pollinated by their reciprocal F-1's with normal cytop lasm. Accordingly, restoration of CMS-D8 by the D8R restorer is conditioned by a single dominant gene (Rf(2)) The genotypes for A, B, and D8R lines in the CMS-DB system are designated S (rf(2)rf(2)), N (rf(2)rf(2)), and S (Rf (2)Rf(2)), respectively. This gametophytic restoration system is potentiall y useful for utilizing F-2 heterosis in cotton.