Pearl millet (Pennisetum glaucum (L.) R. Br.) is grown on about 26 million ha, mostly in the arid and semi-arid tropical regions of Asia and Africa. India is the largest producer of this crop with 9.5 million ha area and more than 7 million tons of grain production. Currently, more than 70 hybrids cultivated on about 5 million ha in India are all based on a single A₁ CMS source, rendering pearl millet hybrid seed industry vulnerable to any disease or insect pest epidemic. Of the several alternative CMS systems identified during the past 40 years, two (A₄ and A₅ ) are of particular interest. Based on the frequency of pollen shedders in isonuclear A-lines in three diverse genetic backgrounds and in six environments, A₅ CMS system was found to be most stable (no pollen shedders), followed by A₄ cytoplasm (0.0 to 0.1% pollen shedders) and A1 cytoplasm (0.0 to 2.5% pollen shedders). Results of a topcross studies with seven diverse populations showed that the average frequency of maintainers was 27% for the A1 cytoplasm, 54% for the A₄ cytoplasm and 96% for the A₅ cytoplasm, indicating the greatest prospects of genetic diversification of A-lines with the A₅ cytoplasm and least with the A₁ cytoplasm. Results also showed that isonuclear hybrids with the A₄ cytoplasm had 5% less mean grain yield than those with the A₁ cytoplasm (P<0.05), but this marginal grain yield disadvantage is overcompensated by more stable male-sterility and higher frequency of maintainers of the A₄ cytoplasm. A similar study showed that there was no significant difference between the mean grain yield of isonuclear hybrids based on the A₁ and the A₅cytoplasm. Thus, seed parent breeding efficiency is likely to be greatest with the A₅5 cytoplasm, followed by the A₄ and the currently commercial A₁ cytoplasm.