Combining ability and heterosis as influenced by male-sterility inducing cytoplasms in sorghum [Sorghum bicolor (L.) Moench]

An investigation was carried out to assess the efficiency of A(2) cytoplasmic-nuclear male-sterility (CMS) system in comparison to the widely used A(1) cytoplasm in terms of general combining ability (gca) effects of male-sterile (A-) lines and mean performance, specific combining ability (sca) effects and mid-parent heterosis of hybrids for days to 50% flowering, plant height and grain yield at International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India in 2001 and 2002 rainy seasons. The material for the study consisted of six pairs of iso-nuclear, allo-plasmic (A(1) and A(2)) A-lines and 36 iso-nuclear hybrids produced by crossing these A-lines with three dual restorer (R-) lines. The results revealed that cytoplasm and its first-order interaction with year, R- and A-lines did not appear to contribute to variation in iso-nuclear hybrids for plant height and grain yield. Cytoplasm had limited effect on gca effects of A-lines and on sca effects and mid-parent heterosis of iso-nuclear hybrids for days to 50% flowering, plant height and grain yield. The mean days to 50% flowering, plant height and grain yield of A(2) cytoplasm-based hybrids were comparable with those of widely used A(1) cytoplasm-based hybrids. The relative frequency of the occurrence of the A(1)- and A(2)-based hybrids with significant sca effects and mid-parent heterosis indicated that A(2) CMS system is as efficient as A(1) with a slight edge over A(1) for commercial exploitation. The implications of these results are discussed in relation to opportunities for broadening not only cytoplasm base but also nuclear genetic base of both the hybrid parents.