Bioscience Method 2024, Vol.15, No.2, 66-75 http://bioscipublisher.com/index.php/bm 70 Figure 2 Development of cassava fibrous and storage roots (Adapted from Sonnewald et al., 2020) Image caption: Cassava is typically propagated using stem cuttings. Nodal-derived fibrous roots emerge within 2–4 days after planting and exhibit primary vascular anatomy with a central vascular cylinder containing star-shaped primary xylem alternating with primary phloem. Around 25–30 days post-planting, secondary root growth begins. These fibrous roots develop a vascular cambium, leading to the formation of new xylem and phloem cells, which eventually break the central vascular cylinder, indicating secondary growth. By 30–40 days, slightly enlarged storage roots with a well-organized vascular cambium between the phloem and xylem can be observed, along with the periderm. Longitudinal vascular rays derived from the cambium bridge the phloem and xylem cells, facilitating the exchange of water, nutrients, and carbohydrates. Storage roots continue to enlarge, forming xylem parenchyma cells for starch and other molecule storage (Adapted from Sonnewald et al., 2020) 4.2 Target traits for genetic improvement The primary target traits for genetic improvement in cassava include increased storage root yield, enhanced starch content, and resistance to pests and diseases. The Cassava Source-Sink project focuses on improving the source-sink relations in cassava to boost its yield potential (Sonnewald et al., 2020). Moreover, genetic engineering efforts aim to address the challenges posed by the crop's long breeding cycle and heterozygous nature. For instance, interspecific pollination with castor bean has been explored to induce and regenerate cassava doubled haploids, which could significantly speed up the breeding process (Baguma et al., 2019a). These efforts are crucial for adapting cassava to changing environmental conditions and ensuring food security in regions dependent on this staple crop. 4.3 Regulatory and ethical considerations The application of genetic engineering in cassava, like in other crops, is subject to regulatory and ethical considerations. Regulatory frameworks ensure that genetically modified organisms (GMOs) are safe for human consumption and the environment. Ethical considerations include the potential impact on biodiversity, the rights of farmers, and the accessibility of genetically engineered crops to smallholder farmers. The Cassava Source-Sink project, for example, operates within a framework that includes confined field trials to assess the safety and efficacy of genetically engineered cassava varieties (Sonnewald et al., 2020). Additionally, the development of genome editing technologies such as CRISPR/Cas9 must consider off-target effects and the long-term implications of genetic modifications (Wang et al., 2019). These considerations are essential to balance the benefits of genetic engineering with the need for responsible and sustainable agricultural practices.
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