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

Abstract

Cytoplasmic male sterile (CMS‐D8) and fertile restorer lines (D8R) of cotton (Gossypium hirsutum L.) (AD1) were developed by transferring the cytoplasm and nuclear gene(s) from G. trilobum (DC.) Skovst. (D8) 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 AD1 and D8 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 F1 and F2 populations with all fertile plants. F1 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 F1'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 F1 plants with D8 cytoplasm were pollinated by their reciprocal F1's with normal cytoplasm. Accordingly, restoration of CMS‐D8 by the D8R restorer is conditioned by a single dominant gene (Rf2). The genotypes for A, B, and D8R lines in the CMS‐D8 system are designated S (rf2rf2), N (rf2rf2), and S (Rf2Rf2), respectively. This gametophytic restoration system is potentially useful for utilizing F2 heterosis in cotton.