International Journal of Horticulture, 2024, Vol.14, No.4, 263-274 http://hortherbpublisher.com/index.php/ijh 264 decisions during the selection process. This technique has been particularly useful in crops like carrots, where traits such as carotenoid content and disease resistance are controlled by complex genetic factors (Ellison et al., 2017; Flores-Ortiz et al., 2020). By integrating MAS into carrot breeding programs, it is possible to develop new varieties that meet the demands of both producers and consumers more efficiently. This study is to develop high-yield and disease-resistant carrot varieties using marker-assisted selection (MAS). By identifying and utilizing molecular markers associated with yield and resistance to major diseases, the breeding process will be streamlined to produce carrot varieties that are both high-yielding and capable of resisting common pathogens. Additionally, the performance of the newly developed carrot varieties will be evaluated in terms of yield, disease resistance, and nutritional quality. This study aims to cultivate carrot varieties that not only possess excellent agronomic traits but also maintain high nutritional quality, thereby contributing to the overall improvement of carrot production and consumption. 2 Basics of Carrot Genetics 2.1 Carrot genome structure The carrot genome is composed of nine chromosomes, which have been mapped using various genetic markers. The development of a saturated genetic linkage map has been instrumental in understanding the carrot genome. For instance, a study using Diversity Arrays Technology (DArT) markers identified 431 markers across nine linkage groups, corresponding to the nine carrot chromosomes (Grzebelus et al., 2013). This mapping has facilitated the identification of key genomic regions associated with important traits, such as the Vrn1 gene on chromosome 2, which governs the biennial growth habit essential for cultivated carrots. Another study utilized high-throughput Simple Sequence Repeat (SSR) mining technology to develop 55,386 markers for the carrot genome, which are associated with protein-coding sequences. The results showed that 51,160 of these markers are single-locus markers, while 4,226 markers can amplify multiple loci. These markers were successfully applied in genome mapping and diversity studies of carrots (Uncu and Uncu, 2019). 2.2 Key genetic traits in carrots Key genetic traits of carrots play a crucial role in improving yield, disease resistance, and quality. In carrot breeding, the genetic mechanism controlling male sterility is a critical area, as it directly impacts the efficiency and cost of hybrid seed production. Male sterility refers to the inability of plant anthers to develop normally, preventing the production of viable pollen and thus avoiding self-pollination. By utilizing this trait, breeders can effectively control the hybridization process, ensuring the purity and consistency of seeds. In recent years, with the advancement of genomics technology, researchers have successfully identified key loci related to male sterility in carrots, providing a scientific basis for more precise breeding (Simon, 2019). By leveraging these loci, breeders can more efficiently select ideal parent materials, significantly improving the efficiency of hybrid variety development. In addition to male sterility, disease resistance is also a core goal in carrot breeding. Carrots are susceptible to various diseases, such as black spot disease and root-knot nematodes, which can severely affect crop yield and quality. In recent years, researchers have identified several key genetic loci related to disease resistance through Quantitative Trait Loci (QTL) analysis. For example, QTLs related to resistance to Alternaria dauci, the pathogen causing carrot leaf blight, have been successfully mapped, providing reliable molecular markers for the development of disease-resistant varieties (Clerc et al., 2015). Moreover, consumer demand for carrot pigments and flavor compounds has also received widespread attention in breeding. Through modern molecular breeding techniques, breeders can more precisely select varieties with excellent quality traits to meet market demand while maintaining high yield and disease resistance in crops (Simon, 2019). 2.3 Genetic diversity in carrot varieties Carrot varieties exhibit a wide range of genetic diversity, which is crucial for breeding programs. Domblides and Domblides (2023) utilized AFLP markers to distinguish eight carrot genotypes with different root colors,
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