Triticeae Genomics and Genetics, 2024, Vol.15, No.2, 88-99 http://cropscipublisher.com/index.php/lgg 91 genes, exhibiting a high phenotypic variance explanation rate. Additionally, a QTL on chromosome 3D showed stable expression across different environments and significantly improved FN, with its effects validated in a doubled haploid population. Guo et al. (2020) study mapped 106 QTLs for protein- and starch-related quality traits, identifying 26 relatively high-frequency QTLs (RHF-QTLs) that were consistent across multiple environments. These findings underscore the potential of QTL mapping in improving wheat quality through targeted breeding programs. Figure 1 A distribution map of QTLs located on wheat chromosomes (Adapteded from Yang et al., 2019) Image caption: The map depicts the specific locations of QTLs associated with thousand grain weight (TGW), grain length (GL), grain width (GW), and grain filling rate (GFR) on different wheat chromosomes; QTLs are represented by bar charts in different colors, showing their coverage on the chromosomes and their overlaps; This visual representation helps breeders understand the genetic control regions of these traits and their potential genetic interactions, thereby enabling more effective use of this information for marker-assisted selection (Adapted from Yang et al., 2019) 3.3 QTL mapping for stress tolerance 3.3.1 Abiotic stress tolerance Abiotic stresses, such as salinity and drought, pose significant challenges to wheat production. A study on salt stress identified 60 QTLs for physiological and biochemical traits, with the B genome contributing the highest number of QTLs under salt stress conditions (Ilyas et al., 2019). This study highlighted the potential of these QTLs for developing salinity-tolerant wheat varieties through MAS. Additionally, a meta-analysis of QTLs for drought tolerance in rice, which shares genomic collinearity with wheat, identified stable QTLs that could be leveraged for improving drought tolerance in wheat (Selamat and Nadarajah, 2021). 3.3.2 Biotic stress tolerance Biotic stress tolerance, including resistance to diseases and pests, is critical for maintaining wheat yield and quality. While the provided data does not include specific studies on biotic stress tolerance in wheat, the principles of QTL mapping and the identification of stable QTLs in other crops, such as rice, can be applied to wheat. For instance, the identification of QTLs for salinity tolerance in rice (Islam et al., 2019) and their potential role in epigenetic modifications (Mazumder et al., 2020) can inform similar approaches in wheat for biotic stress tolerance. In summary, QTL mapping has provided valuable insights into the genetic basis of grain yield, quality, and stress tolerance in wheat. These success stories highlight the potential of QTL mapping to enhance wheat breeding programs and improve crop performance under various environmental conditions. 4 Case Studies 4.1 Recombinant inbred line (RIL) populations Recombinant Inbred Line (RIL) populations have been extensively used in QTL mapping studies to identify genetic loci associated with various traits in wheat. In the study by Goel et al. (2019), 206 recombinant inbred lines (RILs) derived from the wheat varieties WL711 and C306 were cultivated across three different locations in India to evaluate various quality-related traits under different environmental conditions. This research aimed to investigate the genetic control of wheat grain quality traits and map quantitative trait loci (QTLs) to gain a deeper understanding of how genetic factors influence wheat performance in diverse environments (Figure 3) (Hussain et al., 2018).
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