Field Crop 2025, Vol.8, No.2, 51-60 http://cropscipublisher.com/index.php/fc 52 associated with heterosis and optimizing the use of male sterile lines to maximize hybrid performance. The goal is to significantly enhance sorghum productivity, contributing to global food security. 2 Male Sterility in Sorghum 2.1 Types of male sterility Male sterility in sorghum can be broadly categorized into two types: genetic male sterility (GMS) and cytoplasmic male sterility (CMS). Genetic male sterility (GMS): This type of male sterility is controlled by nuclear genes. For instance, the nuclear male sterile (NMS) trait in sorghum is caused by mutations in nuclear genes, as demonstrated by the ms8 mutant, which is a result of a single recessive nuclear gene mutation (Xin et al., 2017). Cytoplasmic male sterility (CMS): CMS is caused by the interaction between the cytoplasmic genome and nuclear genes. It is widely used in hybrid breeding programs. Different CMS systems, such as A1, A2, A3, and others, have been identified in sorghum. The A1 CMS system is the most commonly used in commercial hybrid seed production (Kishan and Borikar, 1989; Choe et al., 2023). 2.2 Mechanisms and genetic basis of male sterility The mechanisms underlying male sterility in sorghum involve complex interactions between nuclear and cytoplasmic genes. Genetic male sterility (GMS): In the case of the ms8 mutant, male sterility is due to defective tapetum development, which leads to the arrest of pollen formation. This mutation is stable across different environments, making it a valuable tool for breeding (Xin et al., 2017). Cytoplasmic male sterility (CMS): The CMS trait is caused by specific interactions between mitochondrial and nuclear genes. For example, the A1 CMS system involves the interaction of mitochondrial genes with nuclear restorer genes (Rf genes). The Rf genes, such as Rf1 and Rf2, are responsible for restoring fertility in CMS plants. The Rf2 gene has been mapped to chromosome SBI-02 and is associated with a pentatricopeptide repeat (PPR) gene family member (Jordan et al., 2010; Narkhede et al., 2022). Additionally, environmental factors can influence the expression of fertility-restoring genes, as seen in the 9E CMS system, where high water availability can up-regulate these genes (Elkonin et al., 2015). 2.3 Previous research on male sterile lines in sorghum breeding Research on male sterile lines in sorghum has significantly contributed to the development of hybrid varieties. Nuclear male sterile lines: The ms8 mutant is a well-characterized nuclear male sterile line that has been shown to be stable across various environments. This line is useful for hybrid breeding and genetic studies (Xin et al., 2017). Cytoplasmic male sterile lines: The A1 CMS system is the most extensively used in commercial hybrid seed production. Studies have identified various restorer genes and their interactions with CMS lines. For instance, the Rf2 gene has been fine-mapped, and its role in fertility restoration has been elucidated (Jordan et al., 2010; Narkhede et al., 2022). Additionally, genetic analyses have shown that CMS systems like A2 and A3 can be utilized for practical breeding programs (Kishan and Borikar, 1989). Marker development: Recent advancements include the development of DNA markers to distinguish between fertile and sterile cytoplasms, facilitating marker-assisted selection in breeding programs (Figure 1). For example, InDel markers have been developed to identify CMS-S and CMS-N cytotypes in sorghum (Choe et al., 2023). 3 Importance of Hybrid Breeding in Sorghum 3.1 Benefits of hybrid sorghum varieties Hybrid sorghum varieties offer several significant advantages over traditional pureline varieties. One of the primary benefits is increased yield. Studies have shown that hybrids can produce greater stalk yield due to taller
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