Effects of supplementing cassava root silage to grazing dairy cows on nutrient utilization, milk production and composition in the tropics.

The current study evaluated the effects of supplementing cassava root silage (CRS) to dairy cows grazing on Megathyrsus maximus cv Mombasa on nutrient intake and digestibility, as well as on milk production and composition. Ten primiparous Girolando cows with average body weight ± (SEM) of 373.45 ± (63.55) kg were used in a replicated 5 × 5 Latin square. Animals were subjected to five treatments: (I) grazing cows without supplementation (WCS); (II) grazing cows provided with 5 kg DM of supplement without CRS (0 g/kg DM of CRS) or including (III) 260, (IV) 520, and (V) 780 g/kg DM of CRS. Statistical analyses were performed using the PROC MIXED of SAS with significance at P < 0.05. Intake of neutral detergent fiber (NDF) and ether extract decreased (P < 0.01), while intake of non-fiber carbohydrates increased (P < 0.01), with increased CRS in the diets. Total DM intake and digestibility of DM, and digestibility of nutritional components were lower (P < 0.03) in WCS animals compared to supplemented animals, except for intake and digestibility of NDF, which was the opposite. Milk yield (MY) and fat corrected milk (FCM), as well as all milk components were unaffected (P > 0.05) by CRS inclusion. In contrast, MY, FCM, protein, lactose, casein, and non-fat milk solids (NFMS) were greater for animals that received supplementation (P < 0.05), compared to animals WCS. Milk fat and total dry extract (TMS) did not differ (P > 0.11) between two groups. In conclusion, CRS may be a potential corn meal replacer in the supplement of dairy cows under tropical conditions.

Genomic and Expression Analysis of Cassava (Manihot esculenta Crantz) Chalcone Synthase Genes in Defense against Tetranychus cinnabarinus Infestation.

Cassava is susceptible to mites, especially Tetranychus cinnabarinus. Secondary metabolism products such as flavonoids play an important role as antimicrobial metabolites protecting plants against biotic stressors including fungal, pathogen, bacterial, and pest defense. The chalcone synthase (CHS) is the initial step of the phenylpropanoid pathway for producing flavonoids and is the gatekeeper of the pathway. Until recently, the CHS genes family has not been systematically studied in cassava. Thirty-nine CHS genes were identified from the cassava genome database. Based on phylogenetic and sequence composition analysis, these CHSs were divided into 3 subfamilies. Within the same subfamily, the gene structure and motif compositions of these CHS genes were found to be quite conserved. Duplication events, particularly segmental duplication of the cassava CHS genes, were identified as one of the main driving force of its expansion. Various cis-elements contained in the promoter might regulate the gene expression patterns of MeCHS. Protein-protein interaction (PPI) network analysis showed that MeCHS1 and MeCHS10 protein are more closely related to other family members. The expression of MeCHS genes in young leaves was higher than that in other tissues, and their expression varies even within the same tissue. Coincidentally, these CHS genes of most LAP subclasses were highly expressed in young leaves. The verified MeCHS genes showed consistent with the real-time reverse transcription quantitative PCR (RT-qPCR) and proteomic expression in protected and affected leaves respectively, indicating that these MeCHS genes play crucial roles in the response to T. cinnabarinus. This study is the first to comprehensively expatiate the information on MeCHS family members. These data will further enhance our understanding both the molecular mechanisms and the effects of CHS genes. In addition, the results will help to further clarify the effects on T. cinnabarinus and provide a theoretical basis for the potential functions of the specific CHS gene in resistance to mites and other biotic stress.

Response of cassava (Manihot esculenta Crantz) genotypes to natural infestation by scale insect pest Stictococcus vayssierei Richard (Hemiptera: Stictococcidae).

Cassava is mostly grown for its starchy roots, which ensure food security. However, it is heavily attacked by the African root and tuber scale (ARTS) Stictococcus vayssierei in Central Africa. This pest is a severe constraint to the production of cassava, food and income security for smallholder farmers. Crop resistance development through the selection of varieties with resistant traits against targeted pests is a promising approach to pest control. This study investigated cassava genotypes' response to natural infestation and determined their resistance levels against S. vayssierei. Six cassava genotypes (two local and four improved) were planted in a completely randomized block design with four replicates. Agronomic parameters and ARTS density were evaluated at 3, 6, 9 and 12 months after planting (MAP). Biochemical content was determined on the pith and cortex of 12 MAP aged tuberous roots. As a result, the improved Excel variety recorded the highest scale density per plant with 102.83 ± 4.14 ARTS/P at 9 MAP. At 12 MAP, high activity of total cyanide (69.18 ± 0.88 and 69.16 ± 1.44 mg/kg) and phenylalanine ammonia-lyase (0.142 ± 0.020 and 0.145 ± 0.010 ΔA/min/mg) were observed in the cortex of the tuberous roots of the improved varieties TMS 96/0023 and TMS 92/0057 which were colonized by the lowest ARTS density. The local variety (Douma) had a high content of total phenols (44.87 ± 1.15 µg/g) in the pith. It also produced the highest yield (23.8 ± 2.9 t ha-1). Varieties TMS 96/0023, TMS 92/0057 and Douma may be the most suitable varieties for the control of ARTS stress.

Cassava molecular genetics and genomics for enhanced resistance to diseases and pests.

Cassava (Manihot esculenta) is one of the most important sources of dietary calories in the tropics, playing a central role in food and economic security for smallholder farmers. Cassava production is highly constrained by several pests and diseases, mostly cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). These diseases cause significant yield losses, affecting food security and the livelihoods of smallholder farmers. Developing resistant varieties is a good way of increasing cassava productivity. Although some levels of resistance have been developed for some of these diseases, there is observed breakdown in resistance for some diseases, such as CMD. A frequent re-evaluation of existing disease resistance traits is required to make sure they are still able to withstand the pressure associated with pest and pathogen evolution. Modern breeding approaches such as genomic-assisted selection in addition to biotechnology techniques like classical genetic engineering or genome editing can accelerate the development of pest- and disease-resistant cassava varieties. This article summarizes current developments and discusses the potential of using molecular genetics and genomics to produce cassava varieties resistant to diseases and pests.

Integrative transcriptomics reveals association of abscisic acid and lignin pathways with cassava whitefly resistance.

BACKGROUND: Whiteflies are a global threat to crop yields, including the African subsistence crop cassava (Manihot esculenta). Outbreaks of superabundant whitefly populations throughout Eastern and Central Africa in recent years have dramatically increased the pressures of whitefly feeding and virus transmission on cassava. Whitefly-transmitted viral diseases threaten the food security of hundreds of millions of African farmers, highlighting the need for developing and deploying whitefly-resistant cassava. However, plant resistance to whiteflies remains largely poorly characterized at the genetic and molecular levels. Knowledge of cassava-defense programs also remains incomplete, limiting characterization of whitefly-resistance mechanisms. To better understand the genetic basis of whitefly resistance in cassava, we define the defense hormone- and Aleurotrachelus socialis (whitefly)-responsive transcriptome of whitefly-susceptible (COL2246) and whitefly-resistant (ECU72) cassava using RNA-seq. For broader comparison, hormone-responsive transcriptomes of Arabidopsis thaliana were also generated. RESULTS: Whitefly infestation, salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA) transcriptome responses of ECU72 and COL2246 were defined and analyzed. Strikingly, SA responses were largely reciprocal between the two cassava genotypes and we suggest candidate regulators. While susceptibility was associated with SA in COL2246, resistance to whitefly in ECU72 was associated with ABA, with SA-ABA antagonism observed. This was evidenced by expression of genes within the SA and ABA pathways and hormone levels during A. socialis infestation. Gene-enrichment analyses of whitefly- and hormone-responsive genes suggest the importance of fast-acting cell wall defenses (e.g., elicitor recognition, lignin biosynthesis) during early infestation stages in whitefly-resistant ECU72. A surge of ineffective immune and SA responses characterized the whitefly-susceptible COL2246's response to late-stage nymphs. Lastly, in comparison with the model plant Arabidopsis, cassava's hormone-responsive genes showed striking divergence in expression. CONCLUSIONS: This study provides the first characterization of cassava's global transcriptome responses to whitefly infestation and defense hormone treatment. Our analyses of ECU72 and COL2246 uncovered possible whitefly resistance/susceptibility mechanisms in cassava. Comparative analysis of cassava and Arabidopsis demonstrated that defense programs in Arabidopsis may not always mirror those in crop species. More broadly, our hormone-responsive transcriptomes will also provide a baseline for the cassava community to better understand global responses to other yield-limiting pests/pathogens.

Microbiome and plant cell transformation trigger insect gall induction in cassava.

Several specialised insects can manipulate normal plant development to induce a highly organised structure known as a gall, which represents one of the most complex interactions between insects and plants. Thus far, the mechanism for insect-induced plant galls has remained elusive. To study the induction mechanism of insect galls, we selected the gall induced by Iatrophobia brasiliensis (Diptera: Cecidomyiidae) in cassava (Euphorbiaceae: Manihot esculenta Crantz) as our model. PCR-based molecular markers and deep metagenomic sequencing data were employed to analyse the gall microbiome and to test the hypothesis that gall cells are genetically transformed by insect vectored bacteria. A shotgun sequencing discrimination approach was implemented to selectively discriminate between foreign DNA and the reference host plant genome. Several known candidate insertion sequences were identified, the most significant being DNA sequences found in bacterial genes related to the transcription regulatory factor CadR, cadmium-transporting ATPase encoded by the cadA gene, nitrate transport permease protein (nrtB gene), and arsenical pump ATPase (arsA gene). In addition, a DNA fragment associated with ubiquitin-like gene E2 was identified as a potential accessory genetic element involved in gall induction mechanism. Furthermore, our results suggest that the increased quality and rapid development of gall tissue are mostly driven by microbiome enrichment and the acquisition of critical endophytes. An initial gall-like structure was experimentally obtained in M. esculenta cultured tissues through inoculation assays using a Rhodococcus bacterial strain that originated from the inducing insect, which we related to the gall induction process. We provide evidence that the modification of the endophytic microbiome and the genetic transformation of plant cells in M. esculenta are two essential requirements for insect-induced gall formation. Based on these findings and having observed the same potential DNA marker in galls from other plant species (ubiquitin-like gene E2), we speculate that bacterially mediated genetic transformation of plant cells may represent a more widespread gall induction mechanism found in nature.

Histological and biophysical changes of cassava roots during retting, a key step of fufu processing.

BACKGROUND: Retting is a key step of cassava processing into widely consumed foods (fufu, chikwangue, miondo and bobolo) in sub-Saharan Africa. For some populations, retting ability is a major quality criterion that drives the adoption of new cassava varieties. Despite this importance, the physiological basis associated with this process remains poorly understood, and should lead to improved screening tools for breeding. Eight cassava varieties contrasting in retting ability properties were used in the present study. Roots and soaking water were sampled during retting and characterized at both histological and biochemical levels. RESULTS: Histological data highlighted the degradation of root cell wall during retting. The average pH of soaking water decreased from 5.94 to 4.31 and the average simple sugars decreased from 0.18 to 0 g L-1 , whereas the organic acids increased up to 5.61 g L-1 . In roots tissue, simple sugars and organic acid contents decreased from 22.9 to 0 g kg-1 and from 80 to 0 g kg-1 , respectively. The total pectin content of roots among varieties at harvest was similar, and decreased during the retting process. Overall, there was a negative correlation between total pectins content and root softening, although this did not reach statistical significance. CONCLUSION: Major histological and biochemical changes occurred during cassava root retting, with some of them associated with the process. Retting affected starch pasting properties more than starch content. Although this process is characterized by root softening and degradation of cell wall structure, the present study strongly suggested that pectin is not the only cell wall component involved in these changes. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Multi-trait selection in multi-environments for performance and stability in cassava genotypes.

Genotype-environment interaction (GEI) presents challenges when aiming to select optimal cassava genotypes, often due to biased genetic estimates. Various strategies have been proposed to address the need for simultaneous improvements in multiple traits, while accounting for performance and yield stability. Among these methods are mean performance and stability (MPS) and the multi-trait mean performance and stability index (MTMPS), both utilizing linear mixed models. This study's objective was to assess genetic variation and GEI effects on fresh root yield (FRY), along with three primary and three secondary traits. A comprehensive evaluation of 22 genotypes was conducted using a randomized complete block design with three replicates across 47 distinct environments (year x location) in Brazil. The broad-sense heritability (H2) averaged 0.37 for primary traits and 0.44 for secondary traits, with plot-based heritability (hmÉ¡2) consistently exceeding 0.90 for all traits. The high extent of GEI variance (σÉ¡xe2) demonstrates the GEI effect on the expression of these traits. The dominant analytic factor (FA3) accounted for over 85% of the total variance, and the communality (ɧ) surpassed 87% for all traits. These values collectively suggest a substantial capacity for genetic variance explanation. In Cluster 1, composed of remarkably productive and stable genotypes for primary traits, genotypes BRS Novo Horizonte and BR11-34-69 emerged as prime candidates for FRY enhancement, while BRS Novo Horizonte and BR12-107-002 were indicated for optimizing dry matter content. Moreover, MTMPS, employing a selection intensity of 30%, identified seven genotypes distinguished by heightened stability. This selection encompassed innovative genotypes chosen based on regression variance index (Sdi2, R2, and RMSE) considerations for multiple traits. In essence, incorporating methodologies that account for stability and productive performance can significantly bolster the credibility of recommendations for novel cassava cultivars.

Water deficit and potassium affect carbon isotope composition in cassava bulk leaf material and extracted carbohydrates.

Cassava (Manihot esculenta Crantz) is an important root crop, which despite its drought tolerance suffers considerable yield losses under water deficit. One strategy to increase crop yields under water deficit is improving the crop's transpiration efficiency, which could be achieved by variety selection and potassium application. We assessed carbon isotope composition in bulk leaf material and extracted carbohydrates (soluble sugar, starch, and cellulose) of selected leaves one month after inducing water deficit to estimate transpiration efficiency and storage root biomass under varying conditions in a greenhouse experiment. A local and improved variety were grown in sand, supplied with nutrient solution with two potassium levels (1.44 vs. 0.04 mM K+) and were subjected to water deficit five months after planting. Potassium application and selection of the improved variety both increased transpiration efficiency of the roots with 58% and 85% respectively. Only in the improved variety were 13C ratios affected by potassium application (up to - 1.8‰ in δ13C of soluble sugar) and water deficit (up to + 0.6‰ in δ13C of starch and soluble sugar). These data revealed a shift in substrate away from transitory starch for cellulose synthesis in young leaves of the improved variety under potassium deficit. Bulk δ13C of leaves that had fully developed prior to water deficit were the best proxies for storage root biomass (r = - 0.62, r = - 0.70) and transpiration efficiency (r = - 0.68, r = - 0.58) for the local and improved variety respectively, making laborious extractions redundant. Results obtained from the youngest fully developed leaf, commonly used as a diagnostic leaf, were complicated by remobilized assimilates in the improved variety, making them less suitable for carbon isotope analysis. This study highlights the potential of carbon isotope composition to assess transpiration efficiency and yield, depending on the chosen sampling strategy as well as to unravel carbon allocation processes.

The Development of Thematic Core Collections in Cassava Based on Yield, Disease Resistance, and Root Quality Traits.

Thematic collections (TCs), which are composed of genotypes with superior agronomic traits and reduced size, offer valuable opportunities for parental selection in plant breeding programs. Three TCs were created to focus on crucial attributes: root yield (CC_Yield), pest and disease resistance (CC_Disease), and root quality traits (CC_Root_quality). The genotypes were ranked using the best linear unbiased predictors (BLUP) method, and a truncated selection was implemented for each collection based on specific traits. The TCs exhibited minimal overlap, with each collection comprising 72 genotypes (CC_Disease), 63 genotypes (CC_Root_quality), and 64 genotypes (CC_Yield), representing 4%, 3.5%, and 3.5% of the total individuals in the entire collection, respectively. The Shannon-Weaver Diversity Index values generally varied but remained below 10% when compared to the entire collection. Most TCs exhibited observed heterozygosity, genetic diversity, and the inbreeding coefficient that closely resembled those of the entire collection, effectively retaining 90.76%, 88.10%, and 88.99% of the alleles present in the entire collection (CC_Disease, CC_Root_quality, and CC_Disease, respectively). A PCA of molecular and agro-morphological data revealed well-distributed and dispersed genotypes, while a discriminant analysis of principal components (DAPC) displayed a high discrimination capacity among the accessions within each collection. The strategies employed in this study hold significant potential for advancing crop improvement efforts.

Cassava (Manihot esculenta Crantz): A Systematic Review for the Pharmacological Activities, Traditional Uses, Nutritional Values, and Phytochemistry.

Cassava (Manihot esculenta Crantz) is considered one of the essential tuber crops, serving as a dietary staple food for various populations. This systematic review provides a comprehensive summary of the nutritional and therapeutic properties of cassava, which is an important dietary staple and traditional medicine. The review aims to evaluate and summarize the phytochemical components of cassava and their association with pharmacological activities, traditional uses, and nutritional importance in global food crises. To collect all relevant information, electronic databases; Cochrane Library, PubMed, Scopus, Web of Science, Google Scholar, and Preprint Platforms were searched for studies on cassava from inception until October 2022. A total of 1582 studies were screened, while only 34 were included in this review. The results of the review indicate that cassava has diverse pharmacological activities, including anti-bacterial, anti-cancer, anti-diabetic, anti-diarrheal, anti-inflammatory, hypocholesterolemic effects, and wound healing properties. However, more studies that aim to isolate the phytochemicals in cassava extracts and evaluate their pharmacological property are necessary to further validate their medical and nutritional values.

Development of cassava core collections based on morphological and agronomic traits and SNPS markers.

Cassava (Manihot esculenta Crantz) holds significant importance as one of the world's key starchy crop species. This study aimed to develop core collections by utilizing both phenotypic data (15 quantitative and 33 qualitative descriptors) and genotypic data (20,023 single-nucleotide polymorphisms) obtained from 1,486 cassava accessions. Six core collections were derived through two optimization strategies based on genetic distances: Average accession-to-nearest-entry and Average entry-to-nearest-entry, along with combinations of phenotypic and genotypic data. The quality of the core collections was evaluated by assessing genetic parameters such as genetic diversity Shannon-Weaver Index, inbreeding (Fis), observed (Ho), and expected (Hs) heterozygosity. While the selection of accessions varied among the six core collections, a seventh collection (consolidated collection) was developed, comprising accessions selected by at least two core collections. Most collections exhibited genetic parameters similar to the complete collection, except for those developed by the Average accession-to-nearest-entry algorithm. However, the variations in the maximum and minimum values of Ho, Hs, and Fis parameters closely resembled the complete collection. The consolidated collection and the collection constructed using genotypic data and the Average entry-to-nearest-entry algorithm (GenEN) retained the highest number of alleles (>97%). Although the differences were not statistically significant (above 5%), the consolidated collection demonstrated a distribution profile and mean trait values most similar to the complete collection, with a few exceptions. The Shannon-Weaver Index of qualitative traits exhibited variations exceeding ±10% when compared to the complete collection. Principal component analysis revealed that the consolidated collection selected cassava accessions with a more uniform dispersion in all four quadrants compared to the other core collections. These findings highlight the development of optimized and valuable core collections for efficient breeding programs and genomic association studies.

New protocol for rapid cassava multiplication in field conditions: a perspective on speed breeding.

Despite the economic and social importance, high-yielding cassava cultivars are only released after extensive research, mainly due to the low multiplication rate. This study aimed to assess the impact of using smaller-sized seed cuttings treated with agrochemicals (8MP) compared to the conventional planting size (16 cm) on genetic parameters, agronomic performance, and the ranking of cassava clones based on yield and growth attributes. The evaluation was carried out in clonal evaluation trial (CET), preliminary yield trial (PYT), and uniform yield trials (UYT). Additionally, a new selection scheme for cassava breeding programs was proposed. A total of 169 clones were evaluated, including 154 improved clones at different stages of selection and 15 local varieties used as checks. Field trials were conducted using both sizes of propagative material (8MP and 16 cm) in each phase of the breeding program. The data were analyzed using mixed models, considering the random effects of genotype and genotype-environment interaction (G×E) to determine variances and heritabilities. Bland-Altman concordance and correlation analysis of selection indices were employed to examine the consistency in the ranking of cassava clones using different seed cutting sizes. The distribution of variance components, heritabilities, means, and range of the 8MP and 16 cm trials in different phases of the cassava breeding program exhibited remarkable similarity, thereby enabling a comparative assessment of similar genetic effects. With a selection intensity of 30%, the concordance in clone ranking was 0.41, 0.57, and 0.85 in CET, PYT, and UYT trials, respectively, when comparing the selection based on 8MP and 16 cm trials. It is worth noting that the ranking of the top 15% remained largely unchanged. Based on the findings, proposed changes in the cassava selection scheme involve increasing the number of trials starting from the CET phase, early incorporation of G×E interaction, elimination of the PYT trial, reduction of the breeding cycle from 5 to 3 years, and a decrease in the time required for variety development from 11 to 9 years. These modifications are expected to lead to cost reduction and enhance the effectiveness of cassava breeding programs.

Volatile Organic Compounds from Cassava Plants Confer Resistance to the Whitefly Aleurothrixus aepim (Goeldi, 1886).

Cassava is an essential tuber crop used to produce food, feed, and beverages. Whitefly pests, including Aleurothrixus aepim (Goeldi, 1886) (Hemiptera: Aleyrodidae), significantly affect cassava-based agroecosystems. Plant odours have been described as potential pest management tools, and the cassava clone M Ecuador 72 has been used by breeders as an essential source of resistance. In this study, we analysed and compared the volatile compounds released by this resistant clone and a susceptible genotype, BRS Jari. Constitutive odours were collected from young plants and analysed using gas chromatography-mass spectrometry combined with chemometric tools. The resistant genotype released numerous compounds with previously described biological activity and substantial amounts of the monoterpene (E)-ß-ocimene. Whiteflies showed non-preferential behaviour when exposed to volatiles from the resistant genotype but not the susceptible genotype. Furthermore, pure ocimene caused non-preferential behaviour in whiteflies, indicating a role for this compound in repellence. This report provides an example of the intraspecific variation in odour emissions from cassava plants alongside information on odorants that repel whiteflies; these data can be used to devise whitefly management strategies. A better understanding of the genetic variability in cassava odour constituents and emissions under field conditions may accelerate the development of more resistant cassava varieties.

Antioxidant Capacity of Polar and Non-Polar Extracts of Four African Green Leafy Vegetables and Correlation with Polyphenol and Carotenoid Contents.

In sub-Saharan Africa, chronic malnutrition is often associated with intestinal inflammation and oxidative stress. African green leafy vegetables (GLVs), commonly consumed by these populations and rich in bioactive compounds, may improve the antioxidant status. The aim of this study was to measure the antioxidant capacity using complementary assays (DPPH, FRAP, ABTS, ORAC and NO scavenging) in polar and non-polar leaf extracts of four African GLVs, cassava (Manihot esculenta), roselle (Hibiscus sabdariffa), jute mallow (Corchorus olitorius), and amaranth (Amaranthus spp.), with spinach (Spinacia oleracea) chosen as a reference. Their antioxidant capacity was correlated with their total polyphenol (TPC), flavonoid (TFC), condensed tannin, lutein, and ß-carotene contents. Identification of phenolic compounds by UHPLC-DAD-MS/MS revealed the presence of three main classes of compound: flavonols, flavones, and hydroxycinnamic acids. Cassava and roselle leaves presented significantly higher TPC and TFC than amaranth, jute mallow, and spinach. They also exhibited the highest antioxidant capacity, even higher than that of spinach, which is known for its important antioxidant effect. The antioxidant capacity was 2 to 18 times higher in polar than non-polar extracts, and was more strongly correlated with TPC and TFC (R > 0.8) than with ß-carotene and lutein contents. These findings provide new data especially for cassava and roselle leaves, for which studies are scarce, suggesting an appreciable antioxidant capacity compared with other leafy vegetables.

Genotype × Environment Interaction and Stability Analysis of Selected Cassava Cultivars in South Africa.

Cassava (Manihot esculenta Crantz) is an important root crop worldwide. It is adapted to a wide range of environmental conditions, exhibiting differential genotypic responses to varying environmental conditions. The objectives of this study were: (1) to examine the effect of genotype, environment and genotype × environment interaction (GEI) on fresh root yield (FRY) and dry matter content (DMC); and (2) to identify superior genotypes that exhibit high performance for the traits of interest using the genetic tools of additive main effects and multiplicative interaction (AMMI) and genotype stability index (GSI) analysis. Eleven cassava genotypes were evaluated in a randomized complete block design at six trial sites in South Africa. The combined analysis of variance based on AMMI revealed significant genotype, environment and GEI for the traits. The percentage variation due to GEI was higher than the percentage variation due to genotype for FRY, reflecting differential genotypic responses across the experimental sites. The proportion of variance due to genotype variation was larger for DMC. Genotype stability index (GSI) showed that UKF3 (G6), 98/0002 (G2) and P4/10 (G5) were the highest yielding and most stable genotypes for FRY, and 98/0002 (G1), UKF3 (G6) and UKF9 (G11) were the highest yielding and most stable genotypes for DMC. Cultivars 98/0002 and UKF3 were identified as providing high stability with superior fresh root yield and DMC. These genotypes could be recommended to farmers for food, feed and industrial applications without the need for further breeding. The AMMI-2 model clustered the testing environments into three mega-environments based on the winning genotypes for FRY and DMC. Mabuyeni (KwaZulu-Natal), Shatale (Mpumalanga) and Mandlakazi (Limpopo) would be the best testing sites in future cassava-genotype evaluation and breeding programs. This study provides a baseline for a future study on the GEI of cassava varieties, using a larger set of genotypes, factoring in seasonal variation.

Effect of sterilants and plant growth regulators in regenerating commonly used cassava cultivars at the Kenyan coast.

Cassava is an important root crop whose seed system is undeveloped. Micropropagation of explants in vitro has the potential of addressing the challenge of the unavailability of healthy cassava planting materials. Therefore, the study determined the effect of sterilization and plant growth regulators on cassava explants to produce certified disease-free plants of commonly used cultivars at the coast of Kenya. The apical nodes drawn from the three cultivars of cassava, Tajirika and Kibandameno and Taita, were used as explants. The sterilant sodium hypochlorite (NaOCl) at 5, 10 and 15% and 70% ethanol for 1 and 5 min and sprayed for 20 s were tested for the effect on the explant. Similarly, the effect of BAP (6-Benzyl amino purine) and NAA (1-Naphthalene acetic acid) Plant Growth Regulators (PGRs) each at 0.5, 1 and 5 mg/L under optimal conditions of sterilization was determined. Surface sterilization using 10% NaOCl followed by spraying 70% ethanol for 20 s had 85% initiation on Tajirika whereas 5% NaOCl followed by spraying 70% ethanol for 20 s had 87% and 91% initiation in Kibandameno and Taita cultivars, respectively. In Tajirika, significantly (p < 0.05) high shooting of 68% was from 5 mg/L BAP in MS media whereas approximately 50% rooting was from either 0.5 mg/L BAP or 5 mg/L NAA in MS media. Kibandameno and Taita cultivars had approximately 50% shooting from MS media without PGRs. Kibandameno had >37% rooting from 0.5 to 5 mg/L BAP or NAA in MS media whereas Taita had approximately 50% rooting from 0 to 5 mg/L NAA in MS media. This protocol showed at least 50% success rate of initiation, shooting and rooting as a rapid multiplication regeneration of Tajirika and Kibandameno and Taita cultivar plantlets with little modification of humidity and temperatures in the growth chambers. This protocol requires validation for use in large-scale production of cassava plantlets to alleviate the inadequacy of cassava planting materials among farmers.

Cassava begomovirus species diversity changes during plant vegetative cycles.

Cassava is a root crop important for global food security and the third biggest source of calories on the African continent. Cassava production is threatened by Cassava mosaic disease (CMD), which is caused by a complex of single-stranded DNA viruses (family: Geminiviridae, genus: Begomovirus) that are transmitted by the sweet potato whitefly (Bemisia tabaci). Understanding the dynamics of different cassava mosaic begomovirus (CMB) species through time is important for contextualizing disease trends. Cassava plants with CMD symptoms were sampled in Lake Victoria and coastal regions of Kenya before transfer to a greenhouse setting and regular propagation. The field-collected and greenhouse samples were sequenced using Illumina short-read sequencing and analyzed on the Galaxy platform. In the field-collected samples, African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), East African cassava mosaic Kenya virus (EACMKV), and East African cassava mosaic virus-Uganda variant (EACMV-Ug) were detected in samples from the Lake Victoria region, while EACMV and East African mosaic Zanzibar virus (EACMZV) were found in the coastal region. Many of the field-collected samples had mixed infections of EACMV and another begomovirus. After 3 years of regrowth in the greenhouse, only EACMV-like viruses were detected in all samples. The results suggest that in these samples, EACMV becomes the dominant virus through vegetative propagation in a greenhouse. This differed from whitefly transmission results. Cassava plants were inoculated with ACMV and another EACMV-like virus, East African cassava mosaic Cameroon virus (EACMCV). Only ACMV was transmitted by whiteflies from these plants to recipient plants, as indicated by sequencing reads and copy number data. These results suggest that whitefly transmission and vegetative transmission lead to different outcomes for ACMV and EACMV-like viruses.

The self-association of cytoplasmic malate dehydrogenase 1 promotes malate biosynthesis and confers disease resistance in cassava.

Malate dehydrogenase (MDH) as an essential metabolic enzyme is widely involved in plant developmental processes. However, the direct relationship between its structural basis and in vivo roles especially in plant immunity remains elusive. In this study, we found that cytoplasmic cassava (Manihot esculenta, Me) MDH1 was essential for plant disease resistance against cassava bacterial blight (CBB). Further investigation revealed that MeMDH1 positively modulated cassava disease resistance, accompanying the regulation of salicylic acid (SA) accumulation and pathogensis-related protein 1 (MePR1) expression. Notably, the metabolic product of MeMDH1 (malate) also improved disease resistance in cassava, and its application rescued the disease susceptibility and decreased immune responses of MeMDH1-silenced plants, indicating that malate was responsible for MeMDH1-mediated disease resistance. Interestingly, MeMDH1 relied on Cys330 residues to form homodimer, which was directly related with MeMDH1 enzyme activity and the corresponding malate biosynthesis. The crucial role of Cys330 residue in MeMDH1 was further confirmed by in vivo functional comparison between overexpression of MeMDH1 and MeMDH1C330A in cassava disease resistance. Taken together, this study highlights that MeMDH1 confers improved plant disease resistance through protein self-association to promote malate biosynthesis, extending the knowledge of the relationship between its structure and cassava disease resistance.

Efficient sugar utilization and transition from oxidative to substrate-level phosphorylation in high starch storage roots of African cassava genotypes.

Cassava's storage roots represent one of the most important sources of nutritional carbohydrates worldwide. Particularly, smallholder farmers in sub-Saharan Africa depend on this crop plant, where resilient and yield-improved varieties are of vital importance to support steadily increasing populations. Aided by a growing understanding of the plant's metabolism and physiology, targeted improvement concepts already led to visible gains in recent years. To expand our knowledge and to contribute to these successes, we investigated storage roots of eight cassava genotypes with differential dry matter content from three successive field trials for their proteomic and metabolic profiles. At large, the metabolic focus in storage roots transitioned from cellular growth processes toward carbohydrate and nitrogen storage with increasing dry matter content. This is reflected in higher abundance of proteins related to nucleotide synthesis, protein turnover, and vacuolar energization in low starch genotypes, while proteins involved in sugar conversion and glycolysis were more prevalent in high dry matter genotypes. This shift in metabolic orientation was underlined by a clear transition from oxidative- to substrate-level phosphorylation in high dry matter genotypes. Our analyses highlight metabolic patterns that are consistently and quantitatively associated with high dry matter accumulation in cassava storage roots, providing fundamental understanding of cassava's metabolism as well as a data resource for targeted genetic improvement.