Tree Genetics and Molecular Breeding 2024, Vol.14, No.1, 22-31 http://genbreedpublisher.com/index.php/tgmb 24 3 Agronomic Traits of Cassava 3.1 Yield-related traits 3.1.1 Root weight and number The root weight and number of cassava are the main indexes to evaluate its yield. Studies have shown that root tuber development and yield are related to a variety of genetic and environmental factors. Okogbenin and Fregene (2002) mentioned that the early expansion of root tuber was closely related to root diameter, dry weight, harvest index and other traits, and the selection of these traits could significantly improve the early yield. In addition, the number and weight of root tubers were positively correlated with the overall growth performance of plants, indicating that the root yield could be effectively increased by improving the overall growth status of plants (Okpara et al., 2014). 3.1.2 Growth rate and growth cycle The growth rate and growth cycle of cassava also have an important impact on its overall yield. Studies have shown that different varieties of cassava have significant differences in growth rate and final yield under different nitrogen fertilizer levels, and these differences reflect the different effects of different genetic backgrounds on environmental resource use efficiency (Phuntupan and Banterng, 2017). In addition, cassava varieties with short growth cycles can reach harvest time faster and are suitable for use in multi-crop rotation systems, thus improving the overall utilization rate of land (Suja et al., 2010). 3.2 Quality-related traits The starch content and quality of cassava are key factors in evaluating its commercial value. Starch yield generally accounts for 20%-35% of cassava dry matter, and there are significant differences among different varieties. The Amylose content of starch affects its gelatinization properties and the quality of the final product. In the study of Ceballos et al. (2007), a cassava natural mutant was found to show abnormally low amylose content, which has higher peak viscosity and lower solubility, showing different potential for industrial applications. The fiber content of cassava root directly affects the taste and digestion of food. The variation of fiber content in cassava root has a direct effect on the grain size distribution and whiteness of processed products, such as flour. Studies have shown that different varieties of cassava have a negative correlation between fiber content and whiteness of treated flour (Chisenga et al., 2019). The size and shape of the root is another important factor in determining the value of cassava as a commodity, especially in agricultural markets and processing industries. The size and shape of root tuber are influenced by both genetic and environmental factors, and are closely related to yield and harvest index. For example, it has been found that under certain environmental conditions, the root size of some varieties is larger than that of others, which is extremely important for selecting varieties suitable for specific market needs (Oliveira et al., 2014). 3.3 Stress resistance traits Cassava is considered to be a highly drought-adaptable crop, with its unique physiological and biochemical mechanisms enabling it to survive and grow under extreme drought conditions. Studies have shown that cassava can reduce water loss in the face of drought stress by adjusting the opening and closing of leaf stomata, while increasing the ability of roots to absorb water from deep soil. In addition, cassava enhances its drought adaptability by regulating photosynthesis and protective enzyme activity, thereby maintaining plant growth and development (Shan et al., 2018). Cassava also shows some resistance to a variety of pests and diseases. Cassava, for example, has been found to have some resistance to red spider mites, mainly through a combination of its growing conditions and the plant's own defense mechanisms. Studies have shown that cassava exhibits high resistance to red spider mites under drought conditions, which may be related to its physiological and biochemical reactions, such as the accumulation of secondary metabolites in the plant (Pratiwi et al., 2022). In addition, cassava improves resistance to pests and diseases by increasing the activity of certain defense enzymes and altering hormone levels in the plant, which provides a possible biomarker for cassava's resistance breeding (Zhao et al., 2015).
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