Stability of male-sterile sources and fertility restoration of their hybrids in pearl millet

Genetic background has a significant effect on the expression of cytoplasmic-nuclear male sterility (CMS) in pearl millet (Pennisetum glaucum (L.) R. Br.). Therefore, a reliable characterization of CMS sources requires the use of near-isonuclear lines and their hybrids. We used this approach to characterize five CMS sources (A₁, A₂, A₃, A_v, and A₄). Male sterility of 81A₄ was the most stable, followed by 81A₁ and 81A_v, indicating the relative merits of these CMS sources in breeding stable male-sterile lines. Male-sterile lines 81A₂ and 81A₃ were highly unstable, indicating their minimal value. Differential male fertility restoration patterns of hybrids made on 81A_V and 81A₄ suggest that the A_v and A₄ cytoplasms represent CMS systems that are different from each other and from A₁, A₂ and A₃. An evaluation of topcross hybrids of 15 diverse populations made on 81A₁ and 81A₄ showed that each population had restorers and maintainers of both cytoplasms and that the frequency of maintainers of A₄ was as high as, or higher than, that of the A₁ cytoplasm. Thus, use of the A₄ cytoplasm can substantially increase the probability of breeding stable male-sterile lines based on inbreds developed from diverse genetic backgrounds, and also provide the opportunity for breeding restorers from each of these diverse genetic sources.