Plant Gene and Trait 2024, Vol.15, No.1, 33-43 http://genbreedpublisher.com/index.php/pgt 37 diversity of cassava is protected by establishing and maintaining a seed bank, and detailed phenotypic and genotypic descriptions of wild and traditional varieties are carried out to improve the understanding and utilization of these resources. Strengthening interdisciplinary cooperation is also an important strategy to promote cassava improvement. Collaboration between plant breeders, geneticists, agronomists and molecular biologists can integrate knowledge and technology from different fields to promote the efficient use of cassava genetic resources. International cooperation is also essential, especially in the context of cassava cultivation in many developing countries around the world, through international projects and research networks that can promote conservation, research and utilization of cassava genetic resources. 4 Case Studies of Marker-assisted Selection 4.1 Successful marker-assisted cassava breeding projects Marker-assisted selection (MAS) has been successfully applied to cassava breeding to increase genetic gain and improve traits such as disease resistance and root quality. A notable example is the introduction of the CMD2 gene from Latin American germplasm into African cassava varieties, where it confers resistance to Mosaic disease. This work, using MAS to pre-select genotypes for the CMD2 gene, resulted in high resistance under field conditions in Africa and has developed 14 genotypes that combine resistance to CMD with high yield and is now in the advanced stages of breeding programmes in Africa (Okogbenin et al., 2007). 4.2 Application of marker-assisted selection in improving cassava yield and quality The application of MAS in cassava is also aimed at improving yield and quality traits. For example, SNP markers associated with increased carotenoid content (Figure 2) and dry matter content (Figure 3) were validated, confirming their effectiveness in multiple genetic contexts. This reinforces their value in cassava biofortification and productivity, contributing to nutritional security and variety performance (Ige et al., 2022). Figure 2 Allelic substitution effects of the markers associated with increased carotenoid content in the (A) breeding, and (B) pre-breeding populations (For marker S5_3387558, the mean and standard deviation cannot be estimated because one genotype had TT) (Adopted from Ige et al., 2022) In addition, Ceballos' group and others at the International Center for Tropical Agriculture have proposed integrating genomic selection (Figure 4) and using inbreeding ancestors (Figure 5) to accelerate genetic gains in cassava, particularly in complex traits such as fresh root yield and starch content (Ceballos et al., 2015). In conclusion, the practical application of MAS in cassava breeding shows that it has the potential to make a significant contribution to the development of improved varieties with increased resistance to disease, higher yields and better quality, thereby supporting food security and agricultural development.
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