Recent Biotechnological Advances in the Improvement of Cassava

Abstract

Cassava (Manihot esculenta Crantz) is the fourth most important source of carbohydrates for human consumption in the tropics and thus occupies a uniquely important position as a food security crop for smallholder farmers. Consequently, cassava improvement is of high priority to most national agricultural research institutions in the tropics. With advances in functional genomics and genome editing approaches in this post genomics era, there are unprecedented opportunities and potential to accelerate the improvement of this important crop. These new technologies will need to be directed toward addressing major cassava production constraints, notably virus resistance, protein content, tolerance to drought and reduction of hydrogen cyanide content. Here, we discuss the important role novel functional genomics and genome editing technologies have and will continue to play in cassava improvement efforts. These approaches, including artificial miRNA (amiRNA), trans-acting small interfering RNA (tasiRNA), clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (Cas9), and Targeting Induced Local Lesions IN Genomes (TILLING), have been shown to be effective in addressing major crop production constraints. In addition to reviewing specific applications of these technologies in cassava improvement, this chapter discusses specific examples being deployed in the amelioration of cassava or of other crops that could be applied to cassava in future.

Genome Editing in Agriculture: Technical and Practical Considerations

“…Cotyledons are an alternative explant, but the transformation and regeneration frequencies are even lower [212]. Because both genetic transformation and conventional breeding are challenging in cassava, genome editing is of particular interest [213]. Odipio et al [174] used CRISPR/Cas9 to knock out pds in cassava and achieved an unanticipated efficiency of 93%–95% regenerated plants with the associated albino phenotype.…”

Farmers’ knowledge, attitudes and practices towards management of cassava pests and diseases in forest transition and Guinea savannah agro-ecological zones of Ghana

“…Crop production, especially cassava, is an important economic activity in Ghana and the world at large. It serves as food for 800 million people in the world ( Fondong & Rey, 2018 ). Ghana is the third leading cassava producer in Africa and with a world share of 6.3%, it ranks sixth in terms of value and volumes.…”

“…Cassava diseases are reported to cause losses of fresh roots as well as planting material. Reduction in root yields could differ considerably with the cassava cultivars’ vulnerability, changes in climate and the inoculum pressure ( Fondong & Rey, 2018 ; Kintché et al ., 2017 ). Pest and disease spread have been on the increase due to cross-border trade, movement of people from one country to another and the sharing of planting materials amongst producers and countries resulting from regional integration ( Echodu et al ., 2019 ).…”

Susceptibility to South African cassava mosaic virus is Associated with a RING Finger E3 Ubiquitin Ligase

“…CMD can result in yield losses of up to 100% in Africa alone (FAO, 2013), with major regional pandemics causing major food security destabilisation such as occurred in East and Central Africa in the 1990s (Legg and Thresh, 2000;Legg et al, 2006). Certain cassava genotypes exhibit resistance or tolerance to cassava mosaic begomoviruses, such as tropical M. esculenta 3 (TME3) and Tropical Manihot Series (TMS) 96/0023, whereas others (T200, TMS 8017) are susceptible to the virus and do not recover from infection (Rogans et al, 2016;Fondong and Rey, 2018). CMD resistance can be polygenic as is the case for CMD1 in wild cassava (Manihot glaziovii), reportedly monogenic dominant as in CMD2 in certain West African cassava landraces (Akano et al, 2002), or a cross of CMD1 and CMD2 to produce CMD3 (Lokko et al, 2006).…”

“…Genetic modi cation of cassava for introduction of resistance traits has been hampered by the plant's recalcitrance to transformation (Zainuddin et al, 2012;Lentz et al, 2018). It has been posited that the use of 21st century genetic engineering (GE) or editing techniques such as arti cial miRNA, transactivating siRNA, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), to improve native antiviral mechanisms, can confer virus resistance without adverse effects on the plant (Vanderschuren et al, 2006;Fondong & Rey 2018). However, this will depend on an intimate understanding of the molecular processes of existing innate antiviral mechanisms, such as the degradation of viral proteins that is directed by the UPS.…”