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 isonuclear hybrids for plant height and grain yield. Cytoplasm had limited effect on gca effects of Alines 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.
The productivity in sorghum is low, owing to various biotic and abiotic constraints. Combining insect resistance with desirable agronomic and morphological traits is important to increase sorghum productivity. Therefore, it is important to understand the variability for various agronomic traits, their heritabilities and nature of gene action to develop appropriate strategies for crop improvement. Therefore, a full diallel set of 10 parents and their 90 crosses including reciprocals were evaluated in replicated trials during the 2013–14 rainy and postrainy seasons. The crosses between the parents with early- and late-flowering flowered early, indicating dominance of earliness for anthesis in the test material used. Association between the shoot fly resistance, morphological, and agronomic traits suggested complex interactions between shoot fly resistance and morphological traits. Significance of the mean sum of squares for GCA (general combining ability) and SCA (specific combining ability) of all the studied traits suggested the importance of both additive and non-additive components in inheritance of these traits. The GCA/SCA, and the predictability ratios indicated predominance of additive gene effects for majority of the traits studied. High broad-sense and narrow-sense heritability estimates were observed for most of the morphological and agronomic traits. The significance of reciprocal combining ability effects for days to 50% flowering, plant height and 100 seed weight, suggested maternal effects for inheritance of these traits. Plant height and grain yield across seasons, days to 50% flowering, inflorescence exsertion, and panicle shape in the postrainy season showed greater specific combining ability variance, indicating the predominance of non-additive type of gene action/epistatic interactions in controlling the expression of these traits. Additive gene action in the rainy season, and dominance in the postrainy season for days to 50% flowering and plant height suggested G X E interactions for these traits.
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