Molecular Plant Breeding 2025, Vol.16, No.1, 1-12 http://genbreedpublisher.com/index.php/mpb 4 4.2 Fruit quality traits Fruit quality traits such as size, shape, flavor, and color are governed by multiple QTLs. A major-effect QTL, FS5.2, was identified for fruit size and shape, influencing both longitudinal and radial growth (Pan et al., 2022). Another study mapped 21 QTLs for fruit shape traits, with consensus QTLs like FS1.1 and FS6.1 playing roles in fruit elongation and diameter, respectively (Zhang et al., 2019). Additionally, QTLs for fruit length and diameter were identified in a high-density genetic map, further elucidating the genetic basis of these traits (Zhu et al., 2016). Understanding the genetic basis of fruit quality traits provides insights into consumer preferences. For instance, the QTL FS5.2, which affects fruit elongation and radial growth, can be targeted to breed cucumbers with desirable shapes (Pan et al., 2022). The identification of QTLs for fruit flavor and color, although less frequently reported, is crucial for developing varieties that meet market demands. The integration of these QTLs into breeding programs can lead to the production of cucumbers with improved taste and visual appeal, enhancing consumer satisfaction (Zhu et al., 2016; Zhang et al., 2019). 4.3 Disease resistance Disease resistance in cucumber is a critical trait for sustainable production. A comprehensive review documented 109 QTLs for disease resistances against seven pathogens, highlighting the extensive genetic resources available for breeding disease-resistant varieties. Specific QTLs for resistance to powdery mildew, downy mildew, and other major diseases have been identified, providing valuable markers for breeding programs (Figure 1) (Wang et al., 2020b). Figure 1 Ruler to the left indicates locations (in Mbp) in the Gy14 V2.0 draft genome assembly (drawn to scale). Vertical black lines are chromosomes. Cloned genes and QTL are aligned to the left and right of each chromosome, respectively. Vertical bar for each QTL represents 1.5 or 2.0 LOD confidence interval on the chromosome. Regions delimited by blue dashed rectangles indicate resistance gene/QTL hot spots or clusters (Adopted from Wang et al., 2020b) The identification of QTLs associated with disease resistance has significant implications for breeding. By incorporating these QTLs into breeding programs, it is possible to develop cucumber varieties with enhanced resistance to multiple pathogens, reducing the reliance on chemical controls and improving crop sustainability. Marker-assisted selection using these QTLs can accelerate the development of resistant varieties, ensuring better yield stability and reduced losses due to diseases (Wang et al., 2020b). 4.4 Growth and development traits Growth and development traits such as plant architecture, flowering time, and growth rate are influenced by various QTLs. For example, QTLs for flowering time and fruit size were identified in the semi-wild
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