Molecular Plant Breeding 2024, Vol.15, No.3, 112-131 http://genbreedpublisher.com/index.php/mpb 121 Multiple studies have identified QTLs associated with fruit quality traits in melon, including sugar and carotenoid content, fruit and seed morphology, and color traits, using high-density genetic maps and recombinant inbred line (RIL) populations (Ramamurthy et al., 2015; Pereira et al., 2018; Galpaz et al., 2018; Zhang et al., 2020; Amanullah et al., 2020). Specific genes within QTL intervals have been pinpointed as candidates for traits like fruit aroma and flesh color, with some studies validating the metabolic activity of these genes (Galpaz et al., 2018). The genetic architecture of fruit quality traits appears to be complex, with many traits being controlled by polygenes and influenced by environmental factors (Zhang et al., 2020; Dantas et al., 2022). Clustering of QTLs on certain chromosomes has been observed, and some QTLs exhibit pleiotropic effects, affecting multiple traits (Zhang et al., 2020; Amanullah et al., 2020). The genetic diversity between wild and cultivated melon varieties, as well as between different botanical groups, provides a rich resource for breeding programs aimed at improving fruit quality and other agronomic traits (Ramamurthy et al., 2015; Maragal et al., 2019). Earliness and ripening behavior, which are important for fruit quality, have been studied through QTL mapping, revealing associations with ethylene emission, fruit firmness, and maturity (Oren et al., 2022). Genotypic and agro-environmental factors, including grafting, water and thermal stress, and targeted nutrition, have been shown to influence fruit quality traits in melon and watermelon (Kyriacou et al., 2018). The synthesis of genomic research in melon has revealed a complex genetic landscape underpinning fruit quality traits. QTL mapping has been instrumental in identifying key genomic regions and candidate genes associated with sweetness, aroma, and texture. These findings are crucial for the development of marker-assisted selection strategies in melon breeding programs. The genetic diversity present in melon varieties, along with the understanding of genotypic and environmental interactions, offers valuable insights for enhancing fruit quality and other desirable traits. 6.1.3 Squash (Cucurbita spp.) The domestication of squash has been a subject of scientific inquiry, focusing on the evolutionary changes and genetic diversity within the Cucurbita genus. Research has explored the morphological, physiological, and genetic alterations that have occurred through the domestication process, revealing the complexity of this transformation. Domestication of Cucurbita maxima involved gene flow between domestic and wild variants, leading to diverse hybrid forms and not a linear evolutionary pathway, with implications for fruit size and seed dormancy patterns (Martinez et al., 2017). Gene expression diversity is generally lower in domesticated species compared to their wild counterparts, affecting a significant portion of the genome and potentially contributing to phenotypic and physiological changes observed in domesticated plants (Liu et al., 2019). Genetic diversity in wild squash Cucurbita argyrosperma subsp. sororia is structured latitudinally along the Mexican Pacific coast, with southern populations exhibiting greater diversity, which has implications for conservation and crop improvement (Balvino-Olvera et al., 2017). The collective research indicates that squash domestication is a dynamic and complex process characterized by extensive hybridization and gene flow, resulting in a wide array of genetic diversity. The decrease in gene expression diversity during domestication may have played a role in the development of domesticated traits. Furthermore, the structured genetic diversity in wild squash populations highlights the importance of regional variation in conservation and agricultural practices.
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