Legume Genomics and Genetics 2024, Vol.15, No.3, 93-104 http://cropscipublisher.com/index.php/lgg 98 200 genes identified as essential for symbiotic nitrogen fixation (SNF) in legumes (Roy et al., 2020). Comparative genomics studies have revealed that nodulation, a critical component of SNF, may have originated from a common ancestor and was subsequently lost in many descendant lineages (Velzen et al., 2018). This finding challenges the traditional view of multiple independent origins of nodulation and suggests a single evolutionary event followed by parallel losses. 5.3 Case studies of specific legume crops Soybean is one of the most extensively studied legume crops, particularly in the context of SNF. Research has identified numerous genes involved in the nodulation process and the regulation of symbiosis in soybean (Roy et al., 2020). Advances in genetic and genomic tools have facilitated the development of soybean varieties with enhanced nitrogen-fixing capabilities and improved resistance to environmental stresses. Chickpea is another important legume crop that has benefited from genetic improvement efforts. The integration of genomics and phenotyping has led to the development of chickpea varieties with improved drought tolerance and pest resistance, which are crucial for maintaining productivity in rainfed regions (Varshney et al., 2018). Additionally, the use of intercropping and crop rotation practices has further enhanced the sustainability and yield of chickpea cultivation (Rodriguez et al., 2020; Kebede, 2021). Lentil cultivation has also seen significant advancements through the application of modern breeding techniques. The development of lentil varieties with enhanced nitrogen-fixing abilities and resilience to environmental stresses has been a key focus of research. Comparative genomics studies have provided insights into the genetic basis of nodulation and SNF in lentils, contributing to the development of improved varieties (Marx et al., 2016; Velzen et al., 2018). In summary, the evolution of agronomic traits in legumes has been driven by the need to enhance yield, pest resistance, and environmental tolerance. The symbiotic relationship with nitrogen-fixing bacteria has played a crucial role in the success of legumes, and ongoing research continues to uncover the genetic and environmental factors that shape this complex trait. Case studies of specific legume crops, such as soybean, chickpea, and lentil, highlight the significant progress made in developing high-yielding and resilient varieties through the integration of modern genomics, phenotyping, and sustainable agricultural practices. 6 Modern Breeding and Biotechnology 6.1 Impact of modern breeding techniques on legume improvement Modern breeding techniques have significantly impacted legume improvement by broadening the genetic base and enhancing desirable traits. Introgression breeding, which involves the incorporation of genetic material from wild relatives into cultivated varieties, has been particularly successful. This method has led to the development of improved cultivars in various legumes such as chickpea, pigeonpea, peanut, lentil, mungbean, urdbean, and common bean. For instance, in mungbean, distant hybridization has resulted in seven improved commercial cultivars, while in urdbean, three such cultivars have been reported (Pratap et al., 2021). Additionally, the use of cytoplasmic male sterility genes from crop wild relatives (CWRs) has significantly benefited pigeonpea breeding (Pratap et al., 2021). The integration of genomics, phenomics, and speed breeding techniques has further accelerated genetic gains in legumes, making them more resilient to environmental stresses and improving their yield potential (Varshney et al., 2018; Singh et al., 2022). 6.2 Role of biotechnology and genetic engineering in legume crop development Biotechnology and genetic engineering have played crucial roles in the development of legume crops by enabling precise modifications at the genetic level. Techniques such as transgenic technology, somatic hybridization, and intragenesis have shown promise in introducing beneficial traits into legume crops. For example, horizontal gene transfer through these biotechnological methods has facilitated the introgression of useful genes, enhancing traits such as disease resistance and stress tolerance (Pratap et al., 2021). The integration of modern genomics approaches, including genome editing tools like CRISPR/Cas9, has further revolutionized legume breeding by
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