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.

DNA fingerprinting reveals varietal composition of Vietnamese cassava germplasm (Manihot esculenta Crantz) from farmers' field and genebank collections.

KEY MESSAGE: A molecular analysis using informative SNP markers in 1570 clones of cassava from Vietnam reveals varietal composition from farmers' field and genebank collections Cassava is the most important smallholder cash crops in Southeast Asia and is especially used in industrial products. Yet, systematic genetic studies on molecular markers from Vietnamese germplasm have not been considered for breeding and conservation programs. We conducted a molecular analysis of 1570 clones of cassava germplasm from farms across six agro-ecological zones using informative SNP markers. We unraveled the genetic diversity and population structure and provided insights into the value of breeding and conservation programs. Duplicated genotypes comprised 98% of the total sample of the Central Highlands region. Ninety-six SNPs were amplified Central Highlands and South East provinces had the highest allelic richness, covering up to 83% of alleles. The average observed heterozygosity (Ho = 0.43) was slightly higher than expected (He = 0.40) across SNP markers, suggesting an excess of heterozygotes plants. Diversity indexes indicated that cassava populations from North West and Eastern Vietnam are genetically diverse (mean He = 0.40). Genetic parentage tests identified 85 unique genetic groups within the varieties KM94, KM419, BRA1305, KM101, KM140, PER262, KM60, KM57 and two unidentified varieties, which accounted for 82% of the frequency distribution. KM94 is the most dominant variety in Vietnamese farms surveyed (38%), reflecting its superior quality and productivity. Discriminant analysis of principal components (DAPC) revealed four main subgroups, which were partially corroborated by neighbor joining (NJ) analyses. After removing duplicates, 31 unique genotypes were distributed across five of the agro-ecological zones. These were well distributed in the subgroups revealed via DAPC and NJ analyses. The genetic groups identified herein could be used to select unique accessions that should ideally conform with ex situ germplasm collections and identify areas where on-farm conservation programs should be targeted. Newly identified genotypes may also contribute as genetic breeding resources that could be used to adapt cassava to future changes and farmers' needs.

A simple PCR-based method for the rapid and accurate identification of spider mites (Tetranychidae) on cassava.

The morphological identification of mites entails great challenges. Characteristics such as dorsal setae and aedeagus are widely used, but they show variations between populations, and the technique is time consuming and demands specialized taxonomic expertise that is difficult to access. A successful alternative has been to exploit a region of the mitochondrial cytochrome oxidase I (COI) gene to classify specimens to the species level. We analyzed the COI sequences of four mite species associated with cassava and classified them definitively by detailed morphological examinations. We then developed an identification kit based on the restriction fragment length polymorphism-polymerase chain reaction of subunit I of the COI gene focused on the three restriction enzymes AseI, MboII, and ApoI. This set of enzymes permitted the simple, accurate identification of Mononychellus caribbeanae, M. tanajoa, M. mcgregori, and Tetranychus urticae, rapidly and with few resources. This kit could be a vital tool for the surveillance and monitoring of mite pests in cassava crop protection programs in Africa, Asia, and Latin America.

Surveillance and diagnostics of the emergent Sri Lankan cassava mosaic virus (Fam. Geminiviridae) in Southeast Asia.

Emergent agricultural pathogens cause severe damage worldwide and their invasive potential is significantly increased by global trade, crop intensification and climate change. Standard surveillance and diagnostic protocols need to be evaluated and implemented, particularly with diseases caused by a wide range of pathogens that induce similar symptoms. Such is the case with Cassava Mosaic Disease (CMD) present in Africa and Asia, and associated with mixed virus infections and recombinant and re-assorted virus strains. CMD has been recently reported in Southeast Asia (SEA) and is already widely spread throughout this region. This communication offers an update on protocols and tools used to track the distribution of CMD and to characterize the pathogen associated with it in SEA.

Reliable molecular identification of nine tropical whitefly species.

The identification of whitefly species in adult stage is problematic. Morphological differentiation of pupae is one of the better methods for determining identity of species, but it may vary depending on the host plant on which they develop which can lead to misidentifications and erroneous naming of new species. Polymerase chain reaction (PCR) fragment amplified from the mitochondrial cytochrome oxidase I (COI) gene is often used for mitochondrial haplotype identification that can be associated with specific species. Our objective was to compare morphometric traits against DNA barcode sequences to develop and implement a diagnostic molecular kit based on a RFLP-PCR method using the COI gene for the rapid identification of whiteflies. This study will allow for the rapid diagnosis of the diverse community of whiteflies attacking plants of economic interest in Colombia. It also provides access to the COI sequence that can be used to develop predator conservation techniques by establishing which predators have a trophic linkage with the focal whitefly pest species.