International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.3, 120-132 http://ecoevopublisher.com/index.php/ijmeb 126 2) Drought Resistance: Cassava’s ability to withstand periods of drought is a critical trait that has been enhanced through selective breeding. Genetic studies have pinpointed alleles involved in water retention and stress response, which are now targets for genetic improvement (Okogbenin et al., 2012; Oliveira et al., 2017). 3) Pest Resistance: As cassava spread across different continents, it faced diverse pest pressures, leading to the selection of pest-resistant varieties. Genetic markers linked to resistance against common pests like the cassava mosaic virus and cassava green mite are particularly valuable for developing resilient cassava strains (Ntui et al., 2023). Hohenfeld et al. (2024) effectively illustrates the comparative resistance of two cassava genotypes to root rot pathogens. The growth data (Panel A) clearly indicates that BRS Kiriris maintains better growth in infested soil compared to BGM-1345. The microscopic analysis (Panels B and C) provides a visual confirmation of the resistance and susceptibility observed, showing less fungal colonization in BRS Kiriris roots. This comprehensive approach, combining growth metrics and microscopic examination, offers valuable insights into the mechanisms of disease resistance in cassava. Such findings are crucial for breeding programs aimed at enhancing cassava resilience against root rot pathogens, ensuring better crop yields. The understanding gained from these phylogenetic studies not only sheds light on the past selection pressures and adaptations but also guides current genetic improvement efforts. By identifying the genetic bases of key adaptive traits, researchers can employ modern biotechnological tools to enhance these characteristics in cassava, ensuring its sustainability and productivity in the face of global change. 4 Case Study: Genetic Adaptation of Cassava to Arid Climates 4.1 Introduction to the specific case study region and its significance Cassava (Manihot esculenta) is a staple crop that plays a crucial role in the food security of millions of people in arid and semi-arid regions. Its ability to produce adequate yields under drought conditions makes it an ideal crop for marginal environments where other crops might fail (Okogbenin et al., 2012). The genetic adaptation of cassava to arid climates is of paramount importance for maximizing productivity potential in these drought-prone areas (Okogbenin et al., 2003). This case study focuses on the genetic traits associated with drought resistance in cassava and the phylogenetic analysis of cassava varieties from arid and non-arid regions, providing insights into the evolutionary trajectories and implications for future breeding programs. 4.2 Genetic traits associated with drought resistance Drought resistance in cassava is a complex, multigenic trait that poses significant challenges for breeding programs. Studies have identified several mechanisms and traits that contribute to drought tolerance, such as early stomatal closure, reduction in photosynthetic proteins, and changes in root morphology (Figure 5) (Zhao et al., 2015; Orek et al., 2020). Additionally, genotypic variability has been observed in cassava’s response to drought stress, with certain varieties demonstrating stronger genetic bases for phenotypic differences in traits like fresh root yield, dry matter content, and harvest index (Okogbenin et al., 2003). A single nucleotide polymorphism in the phytoene synthase gene has been associated with increased provitamin A accumulation in cassava roots, which may also contribute to the crop’s adaptability to arid conditions (Kurniawati et al., 2020). The model drawn by Orek et al. (2020) effectively delineates the complex molecular mechanisms plants use to respond to drought stress. By highlighting the roles of various genes and proteins in both ABA-dependent and ABA-independent pathways, the model provides a comprehensive overview of how plants manage water stress. Understanding these pathways is crucial for genetic and breeding programs aimed at enhancing drought resistance in crops. The clear division between the two pathways and the detailed labeling of involved components make this model a valuable resource for researchers studying plant stress responses.
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