Plant Gene and Trait 2024, Vol.15, No.5, 253-264 http://genbreedpublisher.com/index.php/pgt 259 The artificial inoculation screening for FBR-resistant onion bulbs is a critical step in developing disease-resistant varieties. The method used by Sharma and Cramer (2023) involves directly inoculating the pathogen onto the onion basal plate and creating a high-humidity environment to promote disease development, thus assessing the disease resistance of onion varieties. This screening method accelerates the breeding of resistant varieties, enhances disease resistance in agricultural production, reduces reliance on chemical control, and lowers production costs. The resistant varieties selected through this method can effectively minimize the economic losses caused by FBR in onion production. 6 Improving Yield through Marker-Assisted Breeding 6.1 Yield-related traits and QTLs Yield-related traits in crops are often complex and polygenic, meaning they are controlled by multiple genes and influenced by environmental factors. Quantitative trait loci (QTLs) have been identified as key genetic factors associated with these traits. For instance, wild species of crop plants have been utilized to map QTLs for yield, revealing that these QTLs are distributed across almost all chromosomes, with some regions being more frequently associated with yield traits. This mapping has shown that QTLs for yield and related traits often co-locate, suggesting linkage or pleiotropic effects, and many of these QTLs are stable across different environments and genetic backgrounds (Swamy and Sarla, 2008). In maize, studies have identified and located QTLs associated with grain yield and 24 yield-related traits, demonstrating that different genomic regions contribute to yield through various subsets of these traits. The gene action for these traits varies, with some showing dominant or overdominant effects, while others exhibit mainly additive gene action (Collard et al., 2005). The identification and mapping of QTLs are crucial for understanding the genetic basis of yield-related traits. Advanced backcross QTL analysis has been particularly useful in identifying favorable QTL alleles from wild species while minimizing the impact of unwanted alleles. This approach has been applied successfully in crops like rice and tomato, where stable and consistent major effect yield-enhancing QTLs have been identified. These QTLs are prime targets for marker-assisted selection (MAS), although their context-dependency remains a challenge (Swamy and Sarla, 2008). In maize, the use of molecular markers such as isozymes and restriction fragment length polymorphisms (RFLPs) has enabled the discrimination of individual gene effects, facilitating the elucidation of the numbers and genomic distribution of QTLs involved in yield expression (Collard et al., 2005). 6.2 Breeding for high yield Breeding for high yield involves the strategic use of identified QTLs to enhance the genetic potential of crops. Marker-assisted selection (MAS) is a powerful tool in this regard, allowing breeders to select for favorable alleles associated with high yield. The integration of QTLs from wild species into cultivated varieties has shown promise in improving yield. For example, QTLs identified from wild relatives of rice and tomato have been successfully incorporated into breeding programs, resulting in yield improvements (Swamy and Sarla, 2008). In maize, the identification of QTLs associated with grain yield and related traits has provided valuable insights for breeding programs. The significant associations between marker loci and yield traits highlight the potential for MAS to enhance yield through the manipulation of these QTLs (Collard et al., 2005). The process of breeding for high yield using MAS involves several steps, including the identification of QTLs, validation of their effects in different genetic backgrounds and environments, and the incorporation of these QTLs into breeding lines. The use of advanced backcross QTL analysis has been effective in identifying yield-enhancing QTLs from wild species, which can then be introgressed into elite cultivars. This approach not only improves yield but also helps in maintaining genetic diversity within the breeding pool (Swamy and Sarla, 2008). In maize, the use of molecular markers has facilitated the precise manipulation of QTLs, enabling breeders to enhance yield by selecting for specific genomic regions associated with high yield and its component traits (Collard et al., 2005). 6.3 Evaluation of yield performance The evaluation of yield performance in breeding programs is essential to ensure that the selected QTLs and breeding strategies result in tangible yield improvements. This involves field trials and phenotypic assessments to measure the actual yield and its stability across different environments. In crops like rice and tomato, QTLs
RkJQdWJsaXNoZXIy MjQ4ODYzMg==