Plant Gene and Trait 2024, Vol.15, No.6, 305-313 http://genbreedpublisher.com/index.php/pgt 306 al., 2022). Drought tolerance is another critical trait, as sweet potato is often grown in regions with limited water availability. Drought tolerance mechanisms include changes in antioxidant enzyme activities, chlorophyll and proline concentrations, and nitrate reductase activity, which are correlated with root yield under stress conditions (Laurie et al., 2022). Nutritional composition, particularly the content of essential minerals and dietary fiber, is also a significant trait, with certain cultivars like Bophelo andNdoushowing superior nutritional profiles. 2.2 Genetic diversity of sweet potato The genetic diversity of sweet potato is substantial, with significant variations observed across different regions and cultivars. The sweet potato germplasm collection in Mozambique exhibits high genetic, morphological, and agronomic diversity, comparable to primary centers of origin and other African collections (Hong, 2024). This diversity is crucial for breeding programs aimed at improving drought tolerance and other agronomic traits. The Mozambican germplasm includes genotypes with high potential for drought-prone regions, such as Admarc, Chingova, and NASPOT-5, which can be utilized in breeding programs to enhance drought resistance and yield stability (Maquia et al., 2013). The genetic variability among sweet potato cultivars is also evident in their response to drought stress, with some cultivars showing significant changes in physiological and biochemical traits that contribute to drought tolerance (Laurie et al., 2022). 2.3 Genetic mechanisms of agronomic traits The genetic mechanisms underlying key agronomic traits in sweet potato involve complex interactions between various genes and environmental factors. Drought tolerance, is regulated through multiple signaling pathways that modify growth patterns, activate antioxidants, and accumulate stress proteins (Sapakhova et al., 2023). Marker-assisted selection (MAS) and genome-wide association studies (GWAS) have identified specific genetic markers associated with drought tolerance and other agronomic traits. For instance, transcript and metabolite markers have been used to predict drought tolerance in potato, a related crop, with high accuracy (Sprenger et al., 2017). In sweet potato, similar approaches can be employed to identify and select for drought-tolerant genotypes. The genetic basis of traits like tuber yield involves the interplay of genes controlling vine length, vine weight, and harvest index, which have been shown to have direct and indirect effects on yield (Gervais et al., 2021). Understanding these genetic mechanisms is essential for developing improved sweet potato varieties with enhanced agronomic traits. 3 Overview of Sweet Potato Breeding Methods 3.1 Conventional breeding methods Conventional breeding methods for sweet potatoes typically involve targeted outcrossing followed by phenotypic recurrent selection over multiple generations to identify superior cultivars. This approach relies heavily on field-based phenotyping to evaluate traits such as yield, disease resistance, and quality. Despite its effectiveness, conventional breeding is time-consuming and labor-intensive, often taking several years to develop new cultivars (Slater et al., 2017). 3.2 Molecular breeding methods 3.2.1 Marker-assisted selection (MAS): application examples in sweet potato Marker-assisted selection (MAS) uses DNA markers linked to desirable traits to facilitate the selection process. MAS has been particularly effective for traits controlled by a few major genes, such as disease resistance, MAS has been used to track resistance genes against pathogens like Phytophthora infestans in potatoes, demonstrating its potential for similar applications in sweet potatoes (Beketova et al., 2021). By integrating MAS with conventional breeding, the breeding cycle can be significantly shortened, and the efficiency of selecting superior lines can be improved (Sandhu et al., 2022). 3.2.2 Genomic selection (GS): application of genomic information in sweet potato breeding Genomic selection (GS) is an advanced molecular breeding method that uses genome-wide markers to predict the breeding values of individuals. Unlike MAS, which focuses on specific markers, GS incorporates all available marker information to capture the effects of both major and minor genes. This approach has shown promise in improving complex traits such as yield and stress tolerance in various crops, including sweet potatoes (Varshney
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