Bioscience Method 2024, Vol.15, No.2, 66-75 http://bioscipublisher.com/index.php/bm 67 2 Traditional Breeding Techniques in Cassava 2.1 Conventional breeding approaches Conventional breeding approaches in cassava primarily involve sequential self-pollination to produce inbred or homozygous lines. This method is essential for exposing useful recessive traits and enhancing the breeding value of progenitors. However, the process is notably time-consuming, often taking 10-15 years to achieve the desired homozygosity through successive self-pollination cycles (Lentini et al., 2020). Another traditional method includes cross-pollination, which leverages the genetic diversity of cassava to introduce new traits. However, the heterozygous nature of cassava and its long breeding cycle pose significant challenges to rapid genetic improvement (Baguma et al., 2019b). Cross-pollination is often followed by selection and backcrossing to stabilize the desired traits, which further extends the breeding timeline. 2.2 Limitations of traditional breeding The primary limitation of traditional breeding techniques in cassava is the extensive time required to produce true-breeding lines. The sequential self-pollination method, while effective, is slow and labor-intensive, taking over a decade to achieve homozygosity (Lentini et al., 2020). This slow pace is a significant bottleneck, especially in the context of rapidly changing environmental conditions and the urgent need for climate-resilient cassava varieties. Moreover, the heterozygous nature of cassava complicates the breeding process. The genetic variability inherent in cross-pollinated progeny makes it challenging to stabilize desired traits quickly (Baguma et al., 2019b). This variability necessitates multiple generations of backcrossing and selection, further delaying the development of new varieties. Additionally, traditional breeding methods are limited in their ability to introduce and stabilize complex traits, such as disease resistance and drought tolerance, which are polygenic and require precise genetic manipulation. The reliance on natural genetic variation and the slow pace of conventional breeding make it difficult to keep up with the evolving challenges posed by pests, diseases, and climate change (Baguma et al., 2019b; Lentini et al., 2020). In summary, while conventional breeding approaches have been foundational in cassava improvement, their limitations in terms of time efficiency and genetic precision underscore the need for innovative breeding techniques, such as doubled haploids and genetic engineering, to accelerate the development of improved cassava varieties. 3 Doubled Haploids in Cassava Breeding 3.1 Concept and methods of producing doubled haploids Doubled haploids (DH) are plants that are completely homozygous, achieved by doubling the chromosome number of haploid cells. This technique is highly valuable in plant breeding as it accelerates the development of pure lines, which are essential for hybrid production and genetic studies. The primary methods for producing doubled haploids include anther culture, microspore culture, and in vitro fertilization techniques. These methods have been successfully applied in various crops such as barley, pepper, rapeseed, rice, sugar beet, and wheat (Niazian and Shariatpanahi, 2020; Srividya et al., 2023). In cassava, the potential for producing doubled haploids through gynogenesis has been explored. Gynogenesis involves the in vitro culture of unfertilized ovules or embryos. In a study, female flowers of cassava were bagged to prevent pollination, and early embryo rescue and ovule culture were performed (Figure 1). Although the study did not result in doubled haploids, it provided significant insights into cassava flowering biology and laid the groundwork for future protocol development (Baguma et al., 2019a).
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