Tree Genetics and Molecular Breeding 2024, Vol.14, No.1, 22-31 http://genbreedpublisher.com/index.php/tgmb 25 4 Genetic Basis of Cassava 4.1 Genetic diversity and genetic resources Cassava germplasm resources are very rich, including various local varieties and improved varieties. These germplasm resources play a key role in multiple research and breeding programs around the world, especially in Africa, Latin America and tropical Asia. Cassava germplasm resources not only preserve the genetic diversity of crops, but also provide a basis for the improvement of disease resistance, resistance to retrograde and yield traits. For example, a large number of cassava indigenous varieties and cultivars have been collected and preserved in national breeding programmes in Tanzania, Uganda and Kenya, and these resources show moderate genetic variation and some degree of genetic bottleneck, which has important implications for the development of regional cassava genetic resource conservation strategies (Kawuki et al., 2013). The genetic variation of cassava is very broad, including diversity of morphological characteristics, molecular markers and genetic background. Asare et al. (2011) study in Ghana used morphological descriptors and simple sequence repeat (SSR) markers to analyze the genetic diversity of 43 cassava varieties, which showed significant genetic differences at morphological and molecular levels, providing important information for cassava breeding and germplasm resource management (Figure 1). Figure 1 Dendrogram showing genetic dissimilarity among the cassava accessions based on SSR data (Adopted from Asare et al., 2011) 4.2 Key genetic factors affecting agronomic traits In cassava, multiple quantitative trait loci (QTLs) have been identified, related to productivity, plant structure, and other agronomic traits. For example, one study successfully mapped multiple QTLS that affect cassava production performance and plant building traits, including plant height, branch height, and root yield. These QTLS showed significant genotypic and environmental interactions under different environmental conditions, emphasizing the importance of environmental factors in cassava trait expression (Okogbenin and Fregene, 2003). In the genetic study of cassava, the relationship between phenotype and genotype is the key to understanding the genetic mechanism. Through genome-wide association studies (GWAS), the scientists identified more than 40 QTLS associated with biodefense, quality, and agricultural morphological traits in cassava. Rabbi et al. (2020) not only revealed new genetic loci, but also provided a catalog of favorable SNP markers and candidate genes that could be used in cassava breeding programs, which could help improve cassava agronomic traits and stress resistance (Table 1).
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