Plant Gene and Trait 2024, Vol.15, No.5, 253-264 http://genbreedpublisher.com/index.php/pgt 260 derived from wild species have been evaluated in multiple environments, demonstrating their stable and consistent effects on yield. Such evaluations are crucial for confirming the utility of these QTLs in breeding programs (Swamy and Sarla, 2008). In maize, the evaluation of yield performance has shown that different genomic regions contribute to yield through various traits, and the effects of these regions can vary depending on the genetic context and environmental conditions (Collard et al., 2005). Field trials and phenotypic evaluations provide the necessary data to validate the effectiveness of MAS in improving yield. These evaluations help in identifying the most promising QTLs and breeding lines, which can then be advanced in the breeding pipeline. The use of molecular markers in these evaluations allows for the precise tracking of QTLs and their effects on yield, facilitating the selection of the best-performing lines. In maize, the evaluation of yield performance has highlighted the importance of considering both the genetic and environmental factors influencing yield, ensuring that the selected QTLs provide consistent yield improvements across different conditions (Collard et al., 2005). 7 Integrating Disease Resistance and Yield Improvement 7.1 Combining traits through breeding programs Combining disease resistance and yield improvement in Welsh onion (Allium fistulosum L.) through breeding programs involves the integration of both classical and modern genetic techniques. Classical breeding methods, such as recurrent backcrossing and multi-stage selection, have been traditionally used to introduce and combine desirable traits, including disease resistance and high yield. Recurrent backcrossing is particularly effective for introducing single major genes for disease resistance, while multi-stage selection allows for the simultaneous improvement of multiple traits, including yield and resistance (Miedaner, 2016). The use of molecular markers has revolutionized these breeding programs by enabling the precise targeting of genes and reducing the time required to recover the genome of the recurrent parent (Miedaner, 2016; Padula et al., 2022). Marker-assisted selection (MAS) and genomic selection (GS) are two modern techniques that have significantly enhanced the efficiency of breeding programs. MAS allows for the identification and selection of specific genes or quantitative trait loci (QTL) associated with disease resistance and yield, thereby facilitating the pyramiding of multiple resistance genes and yield-related traits (Miedaner and Korzun, 2012; Cramer et al., 2021). GS, on the other hand, enables the selection of multiple traits directly from the genome using high-throughput genotyping platforms, thus accelerating the breeding process and improving the accuracy of selection (Miedaner and Korzun, 2012; Miedaner, 2016). These advanced techniques have been successfully applied in various crops, including onions, to develop cultivars with enhanced disease resistance and improved yield (Khosa et al., 2016; Sharma and Cramer, 2023). 7.2 Multi-trait selection Multi-trait selection is a critical approach in breeding programs aimed at improving both disease resistance and yield in Welsh onion. This approach involves the simultaneous selection of multiple traits, which can be challenging due to the potential for negative correlations between traits. However, the use of molecular markers and genomic tools has made it possible to overcome these challenges by providing detailed genetic information that can guide the selection process (Miedaner and Korzun, 2012; Miedaner, 2016). For instance, the identification of SNP markers linked to disease resistance and yield traits in onion has facilitated the efficient introgression of these traits into breeding lines (Collins et al., 2018). The integration of multi-trait selection with marker-assisted breeding has shown promising results in various crops. For example, the use of MAS in wheat and barley has enabled the successful selection of multiple disease resistance genes and yield-related traits, leading to the development of high-performing cultivars (Miedaner and Korzun, 2012). Similarly, in onions, the application of MAS and genomic selection has resulted in the identification of germplasm with improved resistance to Fusarium basal rot and enhanced seedling vigor, which are critical traits for yield improvement (Taylor et al., 2019; Sharma and Cramer, 2023). These advancements highlight the potential of multi-trait selection in developing Welsh onion cultivars with superior disease resistance andyield.
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