CMS‐D8 Restoration in Cotton Is Conditioned by One Dominant Gene

Cytoplasmic male sterile (CMS‐D8) and fertile restorer lines (D8R) of cotton ( Gossypium hirsutum L.) (AD 1 ) were developed by transferring the cytoplasm and nuclear gene(s) from G. trilobum (DC.) Skovst. (D 8 ) into the cotton nuclear background. Understanding the genetics of fertility restoration in 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 of D8R restoration to CMS‐D8. The experimental approach involved a series of crossing schemes involving nuclear permutations among the AD 1 and D 8 alloplasms. Eighteen normal genotypes did not restore fertility to the CMS‐D8 (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 pollen also produced all fertile progeny in crosses on A lines. Thus, the D8 restorer functions at the gametophytic level. When heterozygous restored plants were pollinated with B lines, or when reciprocal F 1 's with normal cytoplasm were crossed as male with the A line, the progeny ratio was one fertile to one sterile. A 3:1 ratio was obtained when restored F 1 plants with D 8 cytoplasm were pollinated by their reciprocal F 1 's with normal cytoplasm. 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‐D8 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 potentially useful for utilizing F 2 heterosis in cotton.