Plant Gene and Trait 2024, Vol.15, No.1, 33-43 http://genbreedpublisher.com/index.php/pgt 36 3 Genetic Background and Genetic Resources of Cassava 3.1 Genetic diversity and genomic characteristics of cassava As an important tropical crop, cassava (Manihot esculenta Crantz) is a staple food source for millions of people in many developing countries around the world, as well as an important industrial raw material, and the genetic diversity and genomic characteristics of cassava are critical to improving its agricultural and economic value. The genetic diversity of cassava is manifested in its wide range of morphological characteristics and physiological responses (Gomes et al., 2016), which enable it to adapt to a variety of environmental conditions such as drought and poor soils. The cassava genome is relatively large in size and contains a large number of repeat sequences and transposition elements, which make its genome assembly and analysis challenging. Even so, recent advances in high-throughput sequencing technology have allowed scientists to explore the genomic structure of cassava more deeply, and studies of the cassava genome have revealed a large number of genes related to its stress resistance, growth cycle, and starch accumulation (Gomes et al., 2016), offering the possibility of improving these traits. 3.2 Genetic control of important traits Cassava is an important food and industrial crop in many tropical and subtropical regions of the world. Important traits include yield, starch content, disease resistance and drought tolerance. The genetic control of these traits is complex and is usually influenced by multiple genes, and the expression of these genes is significantly influenced by environmental factors. Understanding the genetic control of cassava traits is crucial to guide breeding and improve crop performance. Yield is one of the most important traits of cassava, which is directly related to the size and weight of the roots. Yield was controlled by multiple quantitative trait loci (QTLs) involved in the regulation of root formation and growth. Starch content is another key, which determines the value of cassava in food and industrial applications (Bechoff et al., 2018). Key enzymes in the starch synthesis pathway, such as ADPG pyrophosphorylase (AGPase) and starch synthetase (SS), have been identified in cassava. Its activity and expression level directly affect the yield and quality of starch. Disease resistance is another important goal in cassava breeding, especially resistance to cassava mosaic virus and cassava bacterial wilt. The genetic basis of these traits involves several genes related to plant immunity, including resistance genes and signaling molecules associated with pathogen interactions, and through traditional genetic analysis and modern molecular marker techniques, researchers have been able to locate some QTLS that control resistance to these diseases (Bechoff et al., 2018). Drought tolerance is a key characteristic of cassava as an important food source in arid areas. Drought tolerance is controlled by multiple genes, involving multiple physiological pathways such as water retention, root development, and plant hormone regulation, and through QTL and genome-wide association studies (GWAS), scientists have identified several candidate genes associated with drought tolerance. 3.3 Existing cassava genetic resources and their utilization strategies Cassava is considered an important pillar of food security and energy production in developing countries because of its good performance in arid and poor soil conditions, and its genetic resources are very rich, including a variety of wild and cultivated species. Wild species tend to possess key traits that cultivated species lack, such as excellent resistance to pests and diseases and adaptability to extreme environments, while cultivated species are superior in terms of yield and food quality. These valuable genetic resources are preserved in multiple gene banks around the globe, such as the International Center for Tropical Agriculture and the Brazilian Agricultural Research Corporation (Embrapa) (Ferguson et al., 2019). In order to make efficient use of these genetic resources, researchers have adopted a variety of strategies, first combining traditional breeding with modern biotechnology (such as marker-assisted selection MAS and CRISPR-Cas9 gene editing technology) to improve cassava agronomic traits, such as increasing yield, enhancing disease resistance, improving nutritional value and processing quality (Ferguson et al., 2019). Further, the genetic
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