International Journal of Horticulture, 2024, Vol.14, No.3, 117-126 http://hortherbpublisher.com/index.php/ijh 122 4.2 Example 1: Enhancing disease resistance in cucumbers through genomic selection Cucurbit viruses, including Potyviruses and Cucumoviruses, pose a significant threat to cucurbit crops worldwide. The identification of natural resistances within the Cucurbitaceae family has been a cornerstone in breeding for disease resistance. Genetic studies have mapped dominant and recessive resistance genes, and markers for marker-assisted selection (MAS) are now available, although higher mapping resolutions are needed for gene identification (Martín-Hernández and Picó, 2020). The development of DNA markers in Cucurbitaceae breeding has been pivotal in constructing genetic linkage maps and consensus maps with phenotypic traits and quantitative trait loci (QTLs), which are essential for MAS in cucurbit breeding programs (Fukino and Kawazu, 2016). 4.3 Example 2: Genetic modification of watermelon for improved drought tolerance The identification of salt-tolerant genotypes within the Cucurbitaceae family is a research priority, especially in the context of climate change and intensive agricultural practices. A greenhouse study assessing the response to salinity in seedlings of various cucurbit genotypes has identified potential candidates for salt-resistant rootstocks, which could be introduced in grafting programs to secure yield stability in salt-affected areas (Modarelli et al., 2020). This approach exemplifies the use of genomic information to select and improve traits such as drought tolerance in watermelon and other cucurbits. 4.4 Example 3: Breeding of bitter gourd with improved fruit quality using marker-assisted selection The transferability of SSR markers from cucumber to other cucurbit crops has been evaluated, demonstrating that cucumber-derived SSR markers can cross-amplify in other species, including bitter gourd. This transferability facilitates the molecular characterization of less studied cucurbit crops and supports genetic diversity analysis, which is crucial for breeding programs aimed at improving fruit quality and other desirable traits (Natenuch et al., 2020). The use of SSR markers in cucurbit breeding has been a breakthrough, allowing for the development of varieties with resistance to multiple diseases and the incorporation of specific horticultural characteristics (Sitterly, 1972). In conclusion, the case studies presented here illustrate the successful implementation of genomic advances in the breeding and improvement of Cucurbitaceae crops. The integration of genetic and genomic resources, such as high-density linkage maps, omics technologies, and DNA markers, has significantly contributed to the development of disease-resistant, drought-tolerant, and high-quality cucurbit varieties. 5 Challenges and Limitations Despite the significant strides in genomic research within the Cucurbitaceae family, several challenges and limitations persist that hinder the full potential of crop improvement and breeding programs. One of the primary challenges is the narrow genetic bases and low variation rates in cucurbit crops, which have led to a breeding bottleneck. This limitation has been a significant obstacle in conventional breeding methods, which, while having contributed to cucurbit production, are now facing diminishing returns (Feng et al., 2023). The development of genetic transformation and gene editing techniques for cucurbit crops has lagged behind other major crops. Although recent progress has been made, the efficiency of these techniques in cucurbits still requires improvement. The screening of germplasm, application of physical treatments, morphogenic genes, and selection markers are areas that need further refinement to enhance genetic transformation efficiency in cucurbit crops (Feng et al., 2023). Another limitation is the availability of genetic and genomic resources for plant improvement. For instance, the construction of saturated molecular linkage maps has been impeded by the narrow genetic base of some cucurbit species, such as cucumber. While the development of highly polymorphic simple sequence repeat (SSR) markers and high-density genetic linkage maps has been reported, these resources are still relatively scarce compared to other crops (Ren et al., 2009). Genomic innovation is crucial for increasing crop production and reducing its impact on ecosystems. However, accessing the large and complex genomes of crops and their wild relatives remains a daunting task. The
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