Cyanogenic, carotenoids and protein composition in leaves and roots across seven diverse population found in the world cassava germplasm collection at CIAT, Colombia

Cassava Breeding and Cultivation Challenges in Thailand: Past, Present, and Future Perspectives

Cassava (Manihot esculenta Crantz) was introduced to Southeast Asia in the 16th-17th centuries and has since flourished as an industrial crop. Since the 1980s, Thailand has emerged as the leading producer and exporter of cassava products. This growth coincided with the initiation of cassava breeding programs in collaboration with the International Center for Tropical Agriculture (CIAT), focusing on root yield and starch production. The success of Thai cassava breeding programs can be attributed to the incorporation of valuable genetic diversity from international germplasm resources to cross with the local landraces, which has become the genetic foundation of many Thai commercial varieties. Effective evaluation under diverse environmental conditions has led to the release of varieties with high yield stability. A notable success is the development of Kasetsart 50. However, extreme climate change poses significant challenges, including abiotic and biotic stresses that threaten cassava root yield and starch content, leading to a potential decline in starch-based industries. Future directions for cassava breeding must include hybrid development, marker-assisted recurrent breeding, and gene editing, along with high-throughput phenotyping and flower induction. These strategies are essential to achieve breeding objectives focused on drought tolerance and disease resistance, especially for CMD and CBSD.

Content and distribution of cyanogenic compounds in cassava roots and leaves in association with physiological age

BACKGROUND

Cassava roots are widely consumed in tropical regions of Asia, Africa, and Latin America. Although the protein, vitamin, carotenoid, and mineral content in the leaves makes them a nutritionally attractive option, their consumption is limited due to their high levels of cyanogenic compounds (CCs). In this study, the CC content in different parts of the plant (leaves, storage root cortex, and parenchyma) was assessed at harvest for 50 landrace genotypes representative of cassava diversity in Latin America. The changes in CC in leaves at different physiological ages (3, 6, 9, and 11 months after planting) were also investigated.

RESULTS

The average CC was higher in the cortex (804 ppm) and leaves (655 ppm) than in root parenchyma (305 ppm). Genotypes from different regions of Latin America, as identified by seven genetic diversity groups, differed significantly in CC levels. The Andean and Amazon groups had, respectively, the lowest (P = 0.0008) and highest (P < 0.0001) CC levels in all three parts of the plants. Cyanogenic compound concentrations were higher in leaves from young plants (P < 0.0001) and decreased with increasing physiological age.

CONCLUSION

The results help to guide the selection of parental lines with low CC levels for breeding and to contribute to the expanded use of cassava and its by-products for food and feed. Cassava for fresh consumption, especially, requires varieties with low total CC content, especially in the root cortex and parenchyma. COL1108 (204, 213, and 174 ppm, respectively, in the parenchyma, cortex, and leaves) and PER297 (83, 238, and 299 ppm, respectively, in the parenchyma, cortex, and leaves) can fulfill this requirement. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

CRISPR-Cas9-mediated knockout of CYP79D1 and CYP79D2 in cassava attenuates toxic cyanogen production

Cassava (Manihot esculenta) is a starchy root crop that supports over a billion people in tropical and subtropical regions of the world. This staple, however, produces the neurotoxin cyanide and requires processing for safe consumption. Excessive consumption of insufficiently processed cassava, in combination with protein-poor diets, can have neurodegenerative impacts. This problem is further exacerbated by drought conditions which increase this toxin in the plant. To reduce cyanide levels in cassava, we used CRISPR-mediated mutagenesis to disrupt the cytochrome P450 genes CYP79D1 and CYP79D2 whose protein products catalyze the first step in cyanogenic glucoside biosynthesis. Knockout of both genes eliminated cyanide in leaves and storage roots of cassava accession 60444; the West African, farmer-preferred cultivar TME 419; and the improved variety TMS 91/02324. Although knockout of CYP79D2 alone resulted in significant reduction of cyanide, mutagenesis of CYP79D1 did not, indicating these paralogs have diverged in their function. The congruence of results across accessions indicates that our approach could readily be extended to other preferred or improved cultivars. This work demonstrates cassava genome editing for enhanced food safety and reduced processing burden, against the backdrop of a changing climate.

Characterization of macro and micro-minerals in cassava leaves from genotypes planted in three different agroecological locations in Nigeria

Diversity in the mineral composition of cassava leaves bred in sub-Saharan Africa has not been fully investigated. This study characterized macro and micro-minerals in 400 genotypes of Cassava leaves planted in three different agroecological environments in Nigeria. Laboratory analysis of the leaves was done using an Inductively Coupled Optical Emission Spectrometer. Across all three locations sampled in this study, the iron content ranged from 43 to 660 mg/kg, zinc from 16 to 440 mg/kg, Manganese 16-61mg/kg, Copper 0.7-14 mg/kg, Aluminum 5.3-630 mg/kg. Among the macro elements, Calcium ranged from 3600 to 17600 mg/kg, Magnesium 1760-6500 mg/kg, Sodium 0.4-720 mg/kg, Potassium 3100-27000 mg/kg. When the location effect was tested, there was a significant difference among the genotypes for all elements. Cluster analysis resulted in five clusters containing 187, 147, 60, 2, and 4 genotypes, respectively. Cluster 2 contained eight varieties (01/0046, 94/0020, 93/0098, 88/112-7(3X), I00/0017, 91/00417, I00/0017, 88/112-7(3X)) that possessed the highest mineral compositions in Fe, Al, Ti, Na, K, S, Mn, and B, respectively. Genotypes 93/0681(4X), 92/0430, and 95/0460 in cluster 3 had the highest concentrations of Mg, Na, and Zn, respectively. The correlation results showed a notable positive relationship among iron with zinc, copper, aluminum, and titanium (r = 0.33, 0.39, 0.48, and 0.56, respectively), zinc with nickel, titanium, and sulphur (r = 0.52, 0.3,2 and 0.51, respectively) while calcium negatively correlated with potassium (r = ‒ 0.31), phosphorus (r = ‒0.41). This study provides evidence that genotypic diversity exists for mineral composition in cassava leaves and, therefore, can be exploited for genetic improvement by breeders seeking solutions to reduce persistent mineral deficiencies in sub-Saharan Africa.

Protein composition, chlorophyll, carotenoids, and cyanide content of cassava leaves (Manihot esculenta Crantz) as influenced by cultivar, plant age, and leaf position

The variation of proximate compositions, amino acids, carotenoids, chlorophyll, and total cyanide contents in cassava leaves was studied to identify the most suitable leaves for human consumption. The cassava leaves from 4 cultivars were analysed at 3 leaf positions as well as at 2 plant ages. The leaves of 'Rayong 5' cultivar from the middle position at 6 months after planting contained the highest crude protein, amino acids, carotenoids, and chlorophyll. The total cyanide content was high and therefore, an effective detoxification method is needed. Protein from the cassava leaves was rich in glutamine, aspartic acid, and leucine, but low in methionine and cysteine. Additionally, cassava leaves were found to be a rich source of carotenoids and chlorophyll. This study provided the evidences that cassava leaves can be an alternative source as protein supplement and for carotenoids and chlorophyll extraction and paves the way to valorise this abundant agricultural by-product.