Molecular Pathogens 2024, Vol.15, No.3, 106-118 http://microbescipublisher.com/index.php/mp 110 There are also regulatory and public acceptance issues associated with some molecular breeding techniques, particularly those involving genetic modification. The use of transgenic plants, where genes from other species are introduced, is subject to strict regulations and can face public resistance due to concerns about safety and environmental impact (Luo et al., 2021; 2023). Even non-transgenic methods like CRISPR/Cas9 can face regulatory hurdles, depending on the country and the specific modifications made (Mapuranga et al., 2022; Jabran et al., 2023). The continuous evolution of pathogens poses a significant challenge to maintaining durable resistance. Pathogens can quickly adapt to overcome resistance genes, necessitating ongoing efforts to identify and deploy new resistance genes. This requires a dynamic and flexible approach to breeding, incorporating the latest genomic tools and knowledge to stay ahead of evolving threats (Hafeez et al., 2021; Mapuranga et al., 2022). While molecular breeding offers significant advantages over traditional methods, it also presents challenges that must be addressed to fully realize its potential. Continued research and innovation in molecular techniques, along with collaboration between researchers, breeders, and policymakers, are essential to overcome these challenges and develop durable disease-resistant wheat cultivars. 4 Genetic Basis of Disease Resistance 4.1 Resistance genes and pathways The genetic basis of disease resistance in wheat involves a complex interplay of major and minor genes, each contributing to the plant's ability to fend off pathogens. Major resistance genes, often referred to as R genes, typically provide high levels of resistance but are vulnerable to being overcome by evolving pathogen races. For instance, genes such as Lr34/Yr18 and Yr36 have been identified as crucial for providing resistance to rust diseases in wheat (Merrick et al., 2011; Mapuranga et al., 2022). These genes encode proteins that are involved in various defense mechanisms, including the production of pathogenesis-related proteins and the activation of defense signaling pathways (Mapuranga et al., 2022). On the other hand, minor genes contribute to quantitative resistance, which is generally more durable but involves a more complex genetic architecture. This type of resistance is controlled by multiple quantitative trait loci (QTL) scattered across the genome, each contributing a small effect (Miedaner et al., 2020; Merrick et al., 2021). For example, resistance to Fusarium head blight (FHB) in wheat is governed by several QTL, such as Fhb1 and Qfhs.ifa-5A, which have been successfully integrated into elite breeding material (Figure 3) (Miedaner and Korzun, 2012). The integration of both major and minor genes is essential for developing wheat cultivars with durable resistance to multiple diseases (Luo et al., 2023). 4.2 Marker-assisted selection Marker-assisted selection (MAS) has revolutionized the breeding of disease-resistant wheat by allowing for the precise selection of resistance genes at the seedling stage, thereby reducing costs and increasing efficiency (Miedaner and Korzun, 2012). MAS is particularly effective for detecting single-major gene resistance, such as the rust resistance genes Lr34 and Yr36, and the eyespot resistance gene Pch1 (Miedaner and Korzun, 2012). However, its application in quantitative disease resistance is more challenging due to the small effects of individual QTL and the prevalence of QTL-background effects (Miedaner and Korzun, 2012; Merrick et al., 2021). Despite these challenges, MAS has been successfully applied in practical breeding programs. For instance, the integration of rust resistance genes Lr34/Yr18 and Lr46/Yr29 into the Australian wheat cultivar 'Stylet' significantly improved its resistance to leaf rust and stripe rust (Kuchel et al., 2007). Similarly, the pyramiding of powdery mildew resistance genes Pm2, Pm4a, and Pm21 into the wheat cultivar 'Yang047' demonstrated the potential of MAS in combining multiple resistance traits (Liu et al., 2000). The future of MAS looks promising with the advent of high-throughput genotyping platforms and chip-based technologies, which are expected to overcome current limitations and open new avenues for molecular-based resistance breeding (Miedaner and Korzun, 2012).
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