Bioscience Method 2024, Vol.15, No.2, 66-75 http://bioscipublisher.com/index.php/bm 69 3.2 Applications in cassava improvement The application of doubled haploids in cassava breeding holds great promise for accelerating genetic gains and developing superior varieties. Doubled haploids can facilitate the rapid production of homozygous lines, which are crucial for hybrid breeding and trait introgression. This technique can significantly shorten the breeding cycle, allowing for faster development of new cassava varieties with desirable traits such as disease resistance, improved yield, and stress tolerance (Li et al., 2020; Srividya et al., 2023). In other crops, doubled haploids have been used to enhance genetic diversity and improve adaptation to changing environmental conditions. For instance, in maize, doubled haploid technology has been integrated with genomic selection to optimize hybrid breeding, resulting in increased efficiency and genetic gain (Li et al., 2020). Similar approaches could be applied to cassava to enhance its breeding programs and develop varieties that are better suited to diverse growing conditions. 3.3 Challenges and opportunities Despite the potential benefits, there are several challenges associated with the production of doubled haploids in cassava. One of the main challenges is the recalcitrance of cassava to in vitro culture regeneration, which has been a significant bottleneck in developing efficient doubled haploid induction protocols (Baguma et al., 2019a; Mabuza et al., 2023). Additionally, the low efficiency of haploid induction and the occurrence of albinism are common issues that need to be addressed (Patial et al., 2022). However, recent advancements in biotechnological tools and genome editing offer new opportunities to overcome these challenges. The use of CRISPR/Cas9 for targeted gene editing and the development of haploid inducer lines could significantly improve the efficiency of doubled haploid production in cassava (Hooghvorst and Nogués, 2020a; 2020b). Moreover, optimizing culture conditions and exploring the use of chemical agents and stress treatments could enhance the induction and regeneration phases of doubled haploid production (Niazian and Shariatpanahi, 2020). In conclusion, while there are challenges in producing doubled haploids in cassava, the potential benefits for cassava breeding are substantial. Continued research and the integration of innovative technologies will be crucial in developing efficient protocols and realizing the full potential of doubled haploids in cassava improvement. 4 Genetic Engineering in Cassava 4.1 Overview of genetic engineering techniques Genetic engineering in cassava involves the manipulation of its genetic material to introduce desirable traits such as increased yield, disease resistance, and improved nutritional content. Techniques such as CRISPR/Cas9 genome editing have been pivotal in this field. The Cassava Source-Sink project exemplifies the integration of genetic engineering with conventional breeding strategies to enhance cassava's storage root and starch yield. This project employs a multi-national pipeline for genetic engineering, covering gene discovery, cloning, transformation, and field trials (Figure 2) (Sonnewald et al., 2020). Additionally, the development of a haploid-inducer mediated genome editing system in maize demonstrates the potential for similar approaches in cassava, where genome-edited haploids can be generated to accelerate breeding cycles (Wang et al., 2019). Sonnewald et al. (2020) examines cassava's source-sink metabolism, highlighting the process from C3 photosynthesis to the development of storage roots. Photoassimilates from leaves are apoplasmically loaded into the phloem and transported to storage roots, where they follow a symplasmic unloading route facilitated by vascular rays. The expression of genes responsible for starch biosynthesis in cassava is similar to those in potato tubers. Challenges in transgenic approaches stem from the complexity of source-sink relationships, single-gene reliance, and environmental variability. However, advancements in mathematical modeling and multi-gene targeting offer new strategies to improve cassava yield. Integrating developmental and metabolic processes is crucial for enhancing source-sink interactions and overall root productivity.
RkJQdWJsaXNoZXIy MjQ4ODY0NQ==