Field Crop 2025, Vol.8, No.2, 51-60 http://cropscipublisher.com/index.php/fc 55 A3 cytoplasmic male-sterile lines in combination with their male-fertile counterparts has been effective in producing high-yielding hybrids (Pfeiffer et al., 2010). Another strategy involves the use of genic male sterility (GMS) systems, where male sterility is controlled by nuclear genes alone. This approach can be enhanced by modern techniques such as CRISPR/Cas-mediated gene editing to create targeted mutations that result in male sterility (Nadeem et al., 2021). Additionally, marker-assisted selection can be employed to identify and select for male sterility genes, as demonstrated in wheat breeding programs (Yang et al., 2021). 4.3 Examples of successful male sterile lines in sorghum Several successful male sterile lines have been developed and utilized in sorghum breeding programs. For instance, the A3 cytoplasmic male-sterile lines 'Dale', 'Wray', 'Sugar Drip', and N100 have been used to create hybrids with higher brix and greater stalk yield, which are advantageous for syrup and ethanol production (Pfeiffer et al., 2010). Another example includes the hybrids derived from cytoplasmic genic male sterile lines such as AKMS 22A x RSSV 9 and BJ 3A x RSSV 9, which have shown superior performance in terms of sweet sorghum quality traits (Indhubala et al., 2010). These examples highlight the potential of male sterile lines in enhancing heterosis and improving the overall productivity of sorghum. 5 Enhancing Heterosis through Male Sterile Lines 5.1 Mechanism of heterosis and how male sterility contributes to hybrid vigor Heterosis, or hybrid vigor, refers to the phenomenon where hybrid offspring exhibit superior qualities compared to their parents. This can include increased yield, improved resistance to diseases, and better adaptability to environmental stresses. The underlying mechanisms of heterosis involve complex genetic interactions, including dominance, overdominance, and epistasis, which result in enhanced performance of hybrids (Kibalnik, 2019). Male sterility, particularly cytoplasmic male sterility (CMS), plays a crucial role in facilitating heterosis. CMS is a maternally inherited trait that prevents the production of functional pollen, thereby necessitating cross-pollination. This ensures that the resulting seeds are hybrids, combining the genetic material of two different parent lines. The use of CMS lines in sorghum breeding has been shown to enhance hybrid vigor by promoting genetic diversity and combining desirable traits from both parents (Kim and Zhang, 2018; Song et al., 2020). 5.2 Crossbreeding experiments to maximize heterosis Crossbreeding experiments are essential to identify the best parental combinations that maximize heterosis. In sorghum, various studies have employed line ×tester mating designs to evaluate the performance of hybrids. For instance, a study involving the crossing of eight restorer lines with five CMS lines in a line × tester design revealed significant heterosis for traits such as plant height, panicle length, and grain yield (Chauhan and Pandey, 2021). Another study conducted in East Africa used 36 pairs of male sterile lines and 42 restorers to generate 121 experimental hybrids. The hybrids were evaluated across multiple locations, and significant heterosis was observed for traits like grain yield and plant height (Ringo et al., 2015). These experiments highlight the importance of selecting genotypically superior parents and evaluating their performance in different environmental conditions to identify the best hybrid combinations. The use of CMS lines in these experiments ensures that the resulting hybrids exhibit enhanced vigor and productivity. 5.3 Case studies or examples of enhanced heterosis in sorghum hybrids using male sterile lines Several case studies have demonstrated the effectiveness of using male sterile lines to enhance heterosis in sorghum hybrids. For example, a study on sweet sorghum hybrids using CMS lines found that male-sterile hybrids had higher brix (sugar content) and greater stalk yield compared to their male-fertile counterparts. The hybrid A3 N100 ×Dale showed positive heterosis for brix, indicating its potential for increased syrup or ethanol production (Pfeiffer et al., 2010). Another study on forage sorghum hybrids revealed significant heterosis for traits such as plant height, leaf length, and green fodder yield. The best crosses, such as ICSA 94 ×Pant Chari-4 and ICSA 94 ×SDSL92111, exhibited superior performance in terms of both quantitative and qualitative traits (Agarwal and Shrotria, 2005).
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