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Cassava is an important root crop that is produced by smallholder farmers across Sub-Saharan Africa. Cassava mosaic disease (CMD), which is caused by a group of cassava mosaic begomoviruses (CMBs), is one of the most devastating diseases of cassava. A previous study showed that SEGS-1 (s equences e nhancing g eminivirus s ymptoms), which occur both in the cassava genome and as episomes during CMD, can increase CMD disease severity and overcome host resistance. In this report, we examined the effects of exogenously applied SEGS-1 on the incidence of CMB infection, symptom severity, and viral DNA copy number in five cassava cultivars that ranged from highly susceptible to highly resistant to CMD. These studies revealed that the effect of SEGS-1 is cultivar dependent. Susceptible cultivars developed severe CMD with or without exogenous SEGS-1, while exogenous SEGS-1 increased disease severity in cultivars carrying CMD2 resistance, which is conferred by a single locus, but not CMD1 resistance, which is polygenic. Analysis of infected plants in the absence of exogenous SEGS-1 revealed that some, but not all, cultivars form SEGS-1 episomes during CMD. The presence of endogenous SEGS-1 episomes in TME14, a CMD2 resistant cultivar, correlated with CMD severity. In contrast, TME3, a closely related CMD2 cultivar, did not produce endogenous SEGS-1 episomes and was more resistance than TME14. The different capacities of TME3 and TME14 to form SEGS-1 episomes is unlikely due to sequence differences in and around their genomic SEGS-1 loci. The functional regions of SEGS-1 were mapped using TME3 to sequences flanking the episome junction, but the junction itself was not required for activity. All cassava cultivars have SEGS-1 sequences in their genomes that have the potential to negatively impact the development of stable CMD resistance by cassava breeding programs. [ABSTRACT FROM AUTHOR]

Cassava is the sixth most important food crop worldwide and the third most important source of calories in the tropics. More than 800 million people depend on this plant's tubers and sometimes leaves. To protect cassava crops and the livelihoods depending on them, we developed a stochastic fractional delayed model based on stochastic fractional delay differential equations (SFDDEs) to analyze the dynamics of cassava mosaic disease, focusing on two equilibrium states, the state of being absent from cassava mosaic disease and the state of being present with cassava mosaic disease. The basic reproduction number and sensitivity of parameters were estimated to characterize the level beyond which cassava mosaic disease prevails or declines in the plants. We analyzed the stability locally and globally to determine the environment that would ensure extinction and its persistence. To support the theoretical analysis, as well as the reliable results of the model, the present study used a nonstandard finite difference (NSFD) method. This numerical method not only improves the model's accuracy but also guarantees that cassava mosaic probabilities are positive and bounded, which is essential for the accurate modeling of the cassava mosaic processes. The NSFD method was applied in all the scenarios, and it was determined that it yields adequate performance in modeling cassava mosaic disease. The ideas of the model are crucial for exploring key variables, which affect the scale of cassava mosaic and the moments of intervention. The present work is useful for discerning the mechanism of cassava mosaic disease as it presents a solid mathematical model capable of determining the stage of cassava mosaic disease. [ABSTRACT FROM AUTHOR]

Sri Lankan cassava mosaic virus (SLCMV) poses a significant threat to global food security by affecting the production of cassava (Manihot esculenta) in South‐east Asia. It causes mosaic patterns on the leaves, disrupts photosynthesis and respiration, and alters carbohydrate accumulation in the tubers. This study aimed to identify proteins associated with cassava mosaic disease symptoms in three cassava cultivars: resistant (TMEB419), tolerant (Kasetsart 50, KU50) and susceptible (Rayong 11, R11) to SLCMV. These cultivars were inoculated with SLCMV using top‐cleft grafting and monitored at 21, 32 and 67 days post‐inoculation (dpi). The disease severity differed among the cultivars following SLCMV inoculation. Liquid chromatography–tandem mass spectrometry (LC–MS/MS)‐based proteomics analysis identified 541 differentially expressed proteins (DEPs), including photosynthesis‐ and respiration‐associated proteins such as RuBisCO large subunit‐binding protein α (LSBP), chlorophyll a‐b binding protein, photosystem I reaction centre subunit III (PSI‐F), glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) and fructose‐bisphosphate aldolase (FBA). A protein–protein interaction network revealed interactions among PSI, PSII, cytochrome complex proteins and electron transporter proteins. Chlorophyll(ide) b reductase NYC1, upregulated in R11 (susceptible) at 21 and 32 dpi, interacted with chlorophyllase‐related proteins, suggesting that it has a role in altering chlorophyll metabolism. Reverse transcription‐quantitative PCR gene expression analysis confirmed upregulation of genes related to photosynthesis and respiration in KU50 and R11, predominantly at 21 or 32 dpi. These findings provide valuable insights into cassava responses to SLCMV infection, especially at the protein level and are key for developing resistant cultivars and effective disease management strategies in future research. [ABSTRACT FROM AUTHOR]

Abstract Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are the two major threats to cassava production in eastern and southern Africa. There have been several interventions over the years in the fight against the two diseases. Whether these interventions have been effective or not can best be answered by continuous and periodic assessment of the diseases. This study was designed to determine the severity, incidence, and distribution of CMD and CBSD and their vector whiteflies in Malawi. Diagnostic surveys were carried out in 16 districts to assess CMD and CBSD parameters on the leaves in 2018. The magnitude of damage on cassava roots caused by CBSD was assessed in 12 districts. The study was designed also to identify alternative hosts for CMD and CBSD. The national mean CMD severity and incidence were 1.6 and 32%, respectively. The national mean CBSD severity and incidence were 1.3 and 75%, respectively. The highest number of whiteflies were recorded in Mangochi district with about 1.8 adult whiteflies per plant in farmer’s fields. There was positive correlation between disease incidence, severity and the number of adult whiteflies for both CMD and CBSD. CMD and CBSD incidence, severity and number of adult whiteflies negatively correlated with altitude. At national level, severity and incidence were higher for CMD than CBSD. CBSD foliar and root incidence and symptom severity were prominent along the shores of lake Malawi. In the contrary, CMD was not confined to the lakeshore areas. Karonga district had the highest CBSD root severity (2.1) and incidence (56%). The national mean percentage of cassava root necrosis was 5.3%. Based on these estimates, Malawi lost about US$ 42.7 million in 2018 due to CBSD root necrosis alone which could be extrapolated to the current cassava production systems. Therefore, it is imperative to improve disease management efforts while also considering the confirmed presence of alternative hosts for CMD in Malawi.

Simple Summary: The whitefly pest, Bemisia tabaci, is an economically important pest given its role in the transmission of plant virus diseases such as cassava mosaic disease (CMD), which continues to devastate cassava productivity in Nigeria. Previous studies have shown that the ability of whiteflies to transmit plant viruses is dependent on several factors, chief of which is its biotype. Given that whiteflies are often morphologically indistinguishable, it is therefore important to explore the genetic diversity of whiteflies towards developing adequate management strategies for CMD in Nigeria. This study therefore investigated the genetic diversity and distribution of B. tabaci genotypes present in cassava farms surveyed across South West and North Central, Nigeria, while also assessing the presence of cassava mosaic begomoviruses (CMBs). The obtained whitefly samples were genotyped using the mitochondrial cytochrome oxidase I (mtCOI) marker. This study identified four genetic groups of B. tabaci, with the Sub-Saharan Africa 1 (SSA1) group being the most predominant. This research also detected African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) in specific subgroups, providing insights for developing improved management strategies to mitigate cassava mosaic disease (CMD) in Nigeria. Whitefly Bemisia tabaci (Gennadium, Hemiptera) causes severe damage to cassava plants through excessive feeding on leaves and transmitting viruses, such as African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and ipomoviruses that cause cassava brown streak disease. Currently, little is known about the molecular diversity and distribution of whitefly species in the major cassava-growing zones of Nigeria. This study aimed to address the knowledge gap by assessing the genetic diversity, distribution, and associated cassava mosaic begomoviruses (CMBs) in whiteflies across South West and North Central, Nigeria. Whitefly samples were systematically collected from cassava plants during georeferenced epidemiological surveys in 2017, 2020, and 2022. The samples were genotyped using the mitochondrial cytochrome oxidase I (mtCOI) marker, and CMBs were detected by PCR with virus-specific primers. Phylogenetic analyses revealed four distinct genetic groups of B. tabaci: Sub-Saharan Africa 1 (SSA1; 84.8%), SSA2 (1.4%), SSA3 (13.1%), and Mediterranean (MED) (0.7%). The SSA1 group was the predominant and most widely distributed genotype across the surveyed zones, with three subgroups identified: SSA1-SG1, SSA1-SG3, and SSA1-SG5. The second most frequently identified genotype, SSA3, was restricted to the North Central zone, along with the SSA2 group, which was only identified in two North Central states (Niger and Plateau). African cassava mosaic virus (ACMV) was detected in SSA1-SG1, SSA1-SG5, and SSA3, whereas EACMV was found in only the SSA1-SG3. The findings of this study will aid in developing better whitefly management strategies to reduce the impact of CMD on cassava production in Nigeria. [ABSTRACT FROM AUTHOR]

Cassava production in Africa is constrained by number of biotic factors, including cassava mosaic disease (CMD). In response to this challenge, the PlantVillage Nuru application, which employs artificial intelligence for CMD diagnosis, provides farmers with the ability to independently detect the disease. This study examines the factors influencing the adoption of the innovative Nuru application by farmers in Benin. Data were randomly collected from 305 farmers in three Agricultural Development Poles (PDAs 5, 6 and 7). A binary logit model was used to analyze the determinants of adoption. The results show that, despite the potential of the Nuru application, the adoption rate remained relatively low at 14.1%. The key drivers of adoption were found to be participation in CMD training, disease knowledge, ownership of an Android smartphone, education level and practice of crop association. These findings emphasize the necessity of intensifying farmers' training and raising awareness about CMD. Effective strategies to reach and train a significant number of farmers are crucial. Enhancing Nuru adoption can lead to more effective CMD management and improved cassava production, which will have a positive impact on food security in Africa and strengthen the resilience of farming communities against biotic challenges. [ABSTRACT FROM AUTHOR]

Cassava is an important root crop that is produced by smallholder farmers across Sub-Saharan Africa. Cassava mosaic disease (CMD), which is caused by a group of cassava mosaic begomoviruses (CMBs), is one of the most devastating diseases of cassava. A previous study showed that SEGS-1 (sequences enhancing geminivirus symptoms), which occur both in the cassava genome and as episomes during CMD, can increase CMD disease severity and overcome host resistance. In this report, we examined the effects of exogenously applied SEGS-1 on the incidence of CMB infection, symptom severity, and viral DNA copy number in five cassava cultivars that ranged from highly susceptible to highly resistant to CMD. These studies revealed that the effect of SEGS-1 is cultivar dependent. Susceptible cultivars developed severe CMD with or without exogenous SEGS-1, while exogenous SEGS-1 increased disease severity in cultivars carrying CMD2 resistance, which is conferred by a single locus, but not CMD1 resistance, which is polygenic. Analysis of infected plants in the absence of exogenous SEGS-1 revealed that some, but not all, cultivars form SEGS-1 episomes during CMD. The presence of endogenous SEGS-1 episomes in TME14, a CMD2 resistant cultivar, correlated with CMD severity. In contrast, TME3, a closely related CMD2 cultivar, did not produce endogenous SEGS-1 episomes and was more resistance than TME14. The different capacities of TME3 and TME14 to form SEGS-1 episomes is unlikely due to sequence differences in and around their genomic SEGS-1 loci. The functional regions of SEGS-1 were mapped using TME3 to sequences flanking the episome junction, but the junction itself was not required for activity. All cassava cultivars have SEGS-1 sequences in their genomes that have the potential to negatively impact the development of stable CMD resistance by cassava breeding programs.

In Côte d'Ivoire, cassava is the source of calories for about 26 million people and generates significant income for stakeholders in the value chain. However, its production is threatened by Cassava Mosaic Disease (CMD), which causes yield losses of up to 70%. This disease remains poorly known among farmers, who often adopt poor cultivation practices that serve to amplify its spread. To address this issue, the Regional Center of Excellence for transboundary plant pathogens Central and West African Virus Epidemiology (WAVE) introduced an innovate android based plant disease detection smart application called "PlantVillage Nuru" to help farmers recognize the disease through real-time diagnosis in cassava fields. The present study analyzes the perceptions and adoption rate of this application by farmers in the diagnosis of CMD within three departments of Côte d'Ivoire. Quantitative and qualitative data were collected from 152 farmers and agricultural technicians, using a questionnaire and interview guide in Dabou, Bouakeé and Man. Data obtained were analyzed through descriptive statistics on SPSS and content analysis. A binary logit regression model was then used to identify the determinants of Nuru application adoption with Stata version 12.1. The study revealed an adoption rate of 45%, focused mainly on monitoring the phytosanitary status of cassava fields (98%), selecting healthy cuttings as planting materials (52%), and accessing agricultural advice (21%). The use of the Nuru application was strongly influenced (P<0.001) by the size of cassava field owned, respondents' participation in WAVE cassava disease awareness activities, the use of family labor, and whether the respondents own or received a smartphone from WAVE. Gender, level of education, the contact with agricultural extension service and internet access, were also significant determinants (P<0.01) in the use of the application. Despite the constraints of smartphone unavailability (65%) and the complexity of using the application (41%) observed, Nuru was considered by farmers (100%) to be an essential and reliable training tool for detecting and managing CMD but did not appear to be needed on a sustained and regular basis. These findings suggest the need for categorization, follow-up, and sustained support to farmers to improve the adoption of agricultural technologies. [ABSTRACT FROM AUTHOR]

Cassava is an important food crop in western Kenya, yet its production is challenged by pests and diseases that require routine monitoring to guide development and deployment of control strategies. Field surveys were conducted in 2022 and 2023 to determine the prevalence, incidence and severity of cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), whitefly numbers and incidence of cassava green mite (CGM) in six counties of western Kenya. Details of the encountered cassava varieties were carefully recorded to determine the adoption of improved varieties. A total of 29 varieties were recorded, out of which 13 were improved, although the improved varieties were predominant in 60% of fields and the most widely grown variety was MM96/4271. The CMD incidence was higher in 2022 (26.4%) compared to 2023 (10.1%), although the proportion of CMD attributable to whitefly infection was greater (50.6%) in 2023 than in 2022 (18.0%). The CBSD incidence in 2022 was 6.4%, while in 2023 it was 4.1%. The CMD incidence was significantly lower (5.9%) for the improved varieties than it was for the local varieties (35.9%), although the CBSD incidence did not differ significantly between the improved (2.3%) and local varieties (9.7%). Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) were both detected. Most infections were single CBSV infections (82.9%), followed by single UCBSV (34.3%) and coinfection with both viruses (16.7%). Whiteflies were more abundant in 2023, in which 28% of the fields had super-abundant populations of >100/plant, compared to 5% in 2022. KASP SNP genotyping designated 92.8% of the specimens as SSA-ECA for 2022, while it was 94.4% for 2023. The cassava green mite incidence was 65.4% in 2022 compared to 79.9% in 2023. This study demonstrates that cassava viruses, whiteflies and cassava green mites continue to be important constraints to cassava production in western Kenya, although the widespread cultivation of improved varieties is reducing the impact of cassava viruses. The more widespread application of high-quality seed delivery mechanisms could further enhance the management of these pests/diseases, coupled with wider application of IPM measures for whiteflies and mites. [ABSTRACT FROM AUTHOR]

Food security is a basic human right that guarantees humans an adequate amount of nutritious food. However, plant viruses and agricultural pests cause real damage to food sources, leading to negative impacts on meeting the human right of obtaining a sufficient amount of food. Understanding infectious disease dynamics can help us to design appropriate control and prevention strategies. Although cassava is among the most produced and consumed crops and greatly contributes to food security, cassava mosaic disease causes a decrease in photosynthesis and reduces cassava yield, resulting in a lack of crops. This paper developed a fractional model for cassava mosaic disease (CMD) dynamics based on the Caputo–Fabrizio (CF) fractional derivative to decrease cassava plant infection. We used fixed-point theory to study the existence of a unique solution in the form of the CMD model. A stability analysis of the model was conducted by using fixed-point theory and the Picard technique. A new numerical scheme was proposed for solving the nonlinear system of a fractional model in the sense of the CF-derivative and applied to obtain numerical simulations for a fractional model of the dynamics of CMD. The obtained results are described using figures that show the dynamics and behaviors of the compartments of CMD, and it is concluded that decreasing the population of whitefly vectors can prevent cassava plants from becoming infected better than increasing the recovery rate of the infected cassava plants. [ABSTRACT FROM AUTHOR]

Abstract Background Cassava mosaic disease (CMD), caused by Sri Lankan cassava mosaic virus (SLCMV) infection, has been identified as a major pernicious disease in Manihot esculenta Crantz (cassava) plantations. It is widespread in Southeast Asia, especially in Thailand, which is one of the main cassava supplier countries. With the aim of restricting the spread of SLCMV, we explored the gene expression of a tolerant cassava cultivar vs. a susceptible cassava cultivar from the perspective of transcriptional regulation and the mechanisms underlying plant immunity and adaptation. Results Transcriptomic analysis of SLCMV-infected tolerant (Kasetsart 50 [KU 50]) and susceptible (Rayong 11 [R 11]) cultivars at three infection stages—that is, at 21 days post-inoculation (dpi) (early/asymptomatic), 32 dpi (middle/recovery), and 67 dpi (late infection/late recovery)—identified 55,699 expressed genes. Differentially expressed genes (DEGs) between SLCMV-infected KU 50 and R 11 cultivars at (i) 21 dpi to 32 dpi (the early to middle stage), and (ii) 32 dpi to 67 dpi (the middle stage to late stage) were then identified and validated by real-time quantitative PCR (RT-qPCR). DEGs among different infection stages represent genes that respond to and regulate the viral infection during specific stages. The transcriptomic comparison between the tolerant and susceptible cultivars highlighted the role of gene expression regulation in tolerant and susceptible phenotypes. Conclusions This study identified genes involved in epigenetic modification, transcription and transcription factor activities, plant defense and oxidative stress response, gene expression, hormone- and metabolite-related pathways, and translation and translational initiation activities, particularly in KU 50 which represented the tolerant cultivar in this study.

Here we investigated the effect of the insect pest whitefly (Bemisia tabaci), cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) on cassava root yield and quality in two cropping seasons 2014–2015 and 2015–2016 on ten cassava varieties in Tanzania. ANOVA (sum of squares or SS) revealed that the time of planting (42.7%) and cassava variety (29.5%) had the largest effect on whitefly population. Not surprisingly, cassava varieties also had the highest effect (SS 39.8 to 70.4%) on both diseases and yield. An increase in whitefly population led to higher disease incidences and severity in 2015–2016 compared to 2014–2015. Some CBSD-resistant and tolerant cassava varieties like Namikonga and Kiroba, respectively, harboured high whitefly populations. The CMD, CBSD and whitefly-susceptible variety, Mreteta, showed highest yield losses of up to 60%, while the resistant variety NDL 2005/1471 had approximately 1% loss. Deployment of varieties resistant to both diseases and whitefly is thus necessary to safeguard cassava production and food security of vulnerable communities in the affected African countries. [ABSTRACT FROM AUTHOR]

Disease resistance gene (R gene)-encoded nucleotide-binding leucine-rich repeat proteins (NLRs) are critical players in plant host defence mechanisms because of their role as receptors that recognise pathogen effectors and trigger plant effector-triggered immunity (ETI). This study aimed to determine the putative role of a cassava coiled-coil (CC)-NLR (CNL) gene MeRPPL1 (Manes.12G091600) (single allele) located on chromosome 12 in the tolerance or susceptibility to South African cassava mosaic virus (SACMV), one of the causal agents of cassava mosaic disease (CMD). A transient protoplast system was used to knock down the expression of MeRPPL1 by clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9). The MeRPPL1-targeting CRISPR vectors and/or SACMV DNA A and DNA B infectious clones were used to transfect protoplasts isolated from leaf mesophyll cells from the SACMV-tolerant cassava (Manihot esculenta) cultivar TME3. The CRISPR/Cas9 silencing vector significantly reduced MeRPPL1 expression in protoplasts whether with or without SACMV co-infection. Notably, SACMV DNA A replication was higher in protoplasts with lower MeRPPL1 expression levels than in non-silenced protoplasts. Mutagenesis studies revealed that protoplast co-transfection with CRISPR-MeRPPL1 silencing vector + SACMV and transfection with only SACMV induced nucleotide substitution mutations that led to altered amino acids in the highly conserved MHD motif of the MeRPPL1-translated polypeptide. This may abolish or alter the regulatory role of the MHD motif in controlling R protein activity and could contribute to the increase in SACMV-DNA A accumulation observed in MeRPPL1-silenced protoplasts. The results herein demonstrate for the first time a role for a CNL gene in tolerance to a geminivirus in TME3. [ABSTRACT FROM AUTHOR]

In Côte d’Ivoire, cassava is the source of calories for about 26 million people and generates significant income for stakeholders in the value chain. However, its production is threatened by Cassava Mosaic Disease (CMD), which causes yield losses of up to 70%. This disease remains poorly known among farmers, who often adopt poor cultivation practices that serve to amplify its spread. To address this issue, the Regional Center of Excellence for transboundary plant pathogens Central and West African Virus Epidemiology (WAVE) introduced an innovate android based plant disease detection smart application called “PlantVillage Nuru” to help farmers recognize the disease through real-time diagnosis in cassava fields. The present study analyzes the perceptions and adoption rate of this application by farmers in the diagnosis of CMD within three departments of Côte d’Ivoire. Quantitative and qualitative data were collected from 152 farmers and agricultural technicians, using a questionnaire and interview guide in Dabou, Bouaké and Man. Data obtained were analyzed through descriptive statistics on SPSS and content analysis. A binary logit regression model was then used to identify the determinants of Nuru application adoption with Stata version 12.1. The study revealed an adoption rate of 45%, focused mainly on monitoring the phytosanitary status of cassava fields (98%), selecting healthy cuttings as planting materials (52%), and accessing agricultural advice (21%). The use of the Nuru application was strongly influenced (P

Cassava production in Africa is constrained by number of biotic factors, including cassava mosaic disease (CMD). In response to this challenge, the PlantVillage Nuru application, which employs artificial intelligence for CMD diagnosis, provides farmers with the ability to independently detect the disease. This study examines the factors influencing the adoption of the innovative Nuru application by farmers in Benin. Data were randomly collected from 305 farmers in three Agricultural Development Poles (PDAs 5, 6 and 7). A binary logit model was used to analyze the determinants of adoption. The results show that, despite the potential of the Nuru application, the adoption rate remained relatively low at 14.1%. The key drivers of adoption were found to be participation in CMD training, disease knowledge, ownership of an Android smartphone, education level and practice of crop association. These findings emphasize the necessity of intensifying farmers’ training and raising awareness about CMD. Effective strategies to reach and train a significant number of farmers are crucial. Enhancing Nuru adoption can lead to more effective CMD management and improved cassava production, which will have a positive impact on food security in Africa and strengthen the resilience of farming communities against biotic challenges.

Mosaic disease spread by the whitefly, Bemisia tabaci, is the major threat to cassava cultivation. This study reveals the variations in cassava whitefly populations across 13 agro-ecological zones of Kerala State, India, and their virulence. Discriminant analysis of morphometric measurements of whitefly pupa from different agro-ecological zones showed more evident distinction compared to adult, and analysis of the whitefly genome using 10 selected ISSR primers has revealed two major clusters within the Sulthan Bathery population, as out group. Sequence analysis of the mitochondrial cytochrome oxidase1 gene showed the presence of two whitefly biotypes, Asia I and Asia II 5. This is the first report of whitefly biotype Asia I infesting cassava. The genetic variation could be the result of isolated speciation under highly diverse elevations and agro-ecological conditions. Cassava plants infested with the Asia I biotype had very low cassava mosaic disease severity compared to those infested with the Asia II 5 biotype. The present study, for the first time, provides molecular evidence of the possibility of more than one biotype of B. tabaci infesting cassava in India. [ABSTRACT FROM AUTHOR]

Introduction: Whitefly (Bemisia tabaci) is a pest of cassava (Manihot esculenta Crantz) and the vector for two of the crop's major viral diseases - cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), causing severe economic losses for farmers. In this context, we conducted an on-farm experiment to study the efficiency of a seed treatment technology containing thiamethoxam, fludioxonil, and metalaxyl for rapid multiplication of superior cassava genotypes and early protection of the crop against whitefly at Salima and Nkhotakota, central Malawi in the 2019/2020 and 2020/2021 cropping seasons, respectively. Methods: The trials were conducted using a randomized complete block design with four replicates. The effect of the application of the seed treatment on stake germination, whitefly population, CMD and CBSD incidences, and stem and storage root yields of three cassava varieties (Kalawe, Mbundumali, and Sauti) at three stake sizes (8 cm, 16 cm, and 25 cm) was compared with control - a 25 cm stake size of each of the cassava variety without seed treatment. A benefit-cost analysis was conducted to determine the profitability of the seed treatment technology for each stake size under certified and non-certified stem scenarios. Results and discussion: Regardless of stake size and variety, plant germination was highest (96% by 16%) and mean whitefly population lowest (adult 0.4 vs. 3.0 plant-1; nymph 1.0 vs. 3.3 plant-1) with seed treatment application than without. Disease incidence measurements showed no significant effect of seed treatment on CBSD control (p = 0.31), but it reduced CMD incidence by 17% vs. 20% in the untreated. Stem and storage root yields across stake size and cassava variety were highest with seed treatment; 489 bundles ha-1 and 10 (DM) Mg ha-1, respectively. Using the 8 cm stake regardless of variety resulted in the highest average benefit-cost ratio for certified (18.3 USD USD-1) and non-certified (7.8 USD USD-1) cassava stem scenarios. Conclusion: We conclude that the application of the seed treatment tested in this study would offer protection to planted stakes, increase their germination, reduce whitefly population, increase stem and storage root yields in areas experiencing whitefly pressure, and result in high economic profits. [ABSTRACT FROM AUTHOR]

IntroductionWhitefly (Bemisia tabaci) is a pest of cassava (Manihot esculenta Crantz) and the vector for two of the crop’s major viral diseases – cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), causing severe economic losses for farmers. In this context, we conducted an on-farm experiment to study the efficiency of a seed treatment technology containing thiamethoxam, fludioxonil, and metalaxyl for rapid multiplication of superior cassava genotypes and early protection of the crop against whitefly at Salima and Nkhotakota, central Malawi in the 2019/2020 and 2020/2021 cropping seasons, respectively.MethodsThe trials were conducted using a randomized complete block design with four replicates. The effect of the application of the seed treatment on stake germination, whitefly population, CMD and CBSD incidences, and stem and storage root yields of three cassava varieties (Kalawe, Mbundumali, and Sauti) at three stake sizes (8 cm, 16 cm, and 25 cm) was compared with control – a 25 cm stake size of each of the cassava variety without seed treatment. A benefit-cost analysis was conducted to determine the profitability of the seed treatment technology for each stake size under certified and non-certified stem scenarios.Results and discussionRegardless of stake size and variety, plant germination was highest (96% by 16%) and mean whitefly population lowest (adult 0.4 vs. 3.0 plant-1; nymph 1.0 vs. 3.3 plant-1) with seed treatment application than without. Disease incidence measurements showed no significant effect of seed treatment on CBSD control (p = 0.31), but it reduced CMD incidence by 17% vs. 20% in the untreated. Stem and storage root yields across stake size and cassava variety were highest with seed treatment; 489 bundles ha-1 and 10 (DM) Mg ha-1, respectively. Using the 8 cm stake regardless of variety resulted in the highest average benefit-cost ratio for certified (18.3 USD USD-1) and non-certified (7.8 USD USD-1) cassava stem scenarios.ConclusionWe conclude that the application of the seed treatment tested in this study would offer protection to planted stakes, increase their germination, reduce whitefly population, increase stem and storage root yields in areas experiencing whitefly pressure, and result in high economic profits.

Cassava mosaic disease (CMD) is caused by a virus transmitted by the whitefly. This disease can destroy cassava at any stage of its growth and it resulted in lower cassava yields. In this paper, we developed a mathematical model for the epidemic of cassava mosaic disease with a deterministic model which has saturation incidence rates. This model aims to explain the effect of vectors on cassava disease outbreaks. First, this model was analyzed using standard dynamic methods to determine the behavior of the solution. We found the existence and condition of disease-free and endemic steady state. The basic reproductive number ($ R_0 $) is obtained by using the next-generation method which $ R_0 $ helps assess the ability to spread infectious diseases. Second, the stability of the steady state was analyzed, then we obtain the condition of existence of local stability and global stability at each steady state of this model. Third, analysis of the sensitivity indices in the threshold number to determine the effect of the various parameters. Finally, the results of the theoretical model were validated by numerical simulations. It is represented by various graphs converging at a steady state and stable.

Cassava production in Ivory Coast is hampered by cassava mosaic disease (CMD), which is caused by several begomovirus species. To increase cassava production and conserve genetic resources, the Centre National de Recherche Agronomique (CNRA) maintains a germplasm collection of 610 cassava accessions of various origins, which is kept in open fields in Bouaké and Man. We carried out an epidemiological assessment of the collection and a molecular characterization of the viruses infecting the CNRA cassava germplasm. The field in Man was less affected by CMD (incidence 49.78%, severity 2.23, whitefly infection 2.23%), despite the abundant whitefly populations (1.34 per plant), compared to Bouaké (incidence 74.54%, severity 2.92, whitefly infection 8.04% and whitefly population of 0.34 per plant). However, the predominant mode of CMD transmission was through infected cassava cuttings at both sites. PCR analysis showed that the East African cassava mosaic Cameroon virus (EACMCMV) was always found in co‐infection with African cassava mosaic virus (ACMV), which also occurred in single infection. Co‐infections of EACMCMV and ACMV were more prevalent in Bouaké (52.64%) than Man (13.87%). Eleven complete genome sequences of cassava mosaic begomoviruses infecting the CNRA germplasm were obtained, and phylogenetic analysis showed that they are closely related to ACMV and EACMCMV isolates from Ghana, Burkina Faso and Nigeria. The results of this study will assist breeders to screen accurately for CMD resistance in progeny resulting from parental lines, enabling the strategic distribution of new clean cassava planting materials to reduce the impact of CMD. [ABSTRACT FROM AUTHOR]

This article reports the first identification of the severe Uganda variant of the East African cassava mosaic virus (EACMV-Ug) in Zambia. Despite previous surveys not finding EACMV-Ug in Zambia, severe symptoms characteristic of the virus have been observed in Zambian fields. Phylogenetic analysis confirmed the presence of EACMV-Ug in Zambia for at least the last decade. Additionally, the study identified recombination events in the coat protein-coding region of EACMV-Ug, which is a novel finding. This report provides valuable information for researchers studying cassava mosaic disease and its impact on cassava crops in sub-Saharan Africa. [Extracted from the article]

Cassava (Manihot esculenta) is a major staple food and the world's fourth source of calories. Biotechnological contributions to enhancing this crop, its advances, and present issues must be assessed regularly. Functional genomics, genomic-assisted breeding, molecular tools, and genome editing technologies, among other biotechnological approaches, have helped improve the potential of economically important crops like cassava by addressing some of its significant constraints, such as nutrient deficiency, toxicity, poor starch quality, disease susceptibility, low yield capacity, and postharvest deterioration. However, the development, improvement, and subsequent acceptance of the improved cultivars have been challenging and have required holistic approaches to solving them. This article provides an update of trends and gaps in cassava biotechnology, reviewing the relevant strategies used to improve cassava crops and highlighting the potential risk and acceptability of improved cultivars in Southern Africa. [ABSTRACT FROM AUTHOR]

In this paper, a fractional-order model including healthy cassava, infected cassava, and infected vectors is proposed to study the transmission dynamics of cassava mosaic disease. Firstly, the non-negativity and boundedness of the solutions in the system and the stability of all feasible equilibrium points of the system are strictly discussed. Hopf bifurcation induced by the disease transmission rate from the vectors to the healthy cassava is studied for the proposed system. Secondly, a novel periodic pulse feedback controller is proposed to suppress the bifurcation phenomenon. The expression of the bifurcation point of the controlled system is given with the help of the linearized average system. It is shown that the stability performance is extremely excellent with the help of the proposed controller and that the control effect is independent of pulse width. Numerical simulations are performed to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Genotype by environment interaction remains a substantial issue in all breeding programs. Crop genotypes are generally developed in a central breeding location, but always require the evaluation of breeding products in different environments. This is particularly relevant in countries that have a wide range of climates. Eighteen cassava genotypes were evaluated in Cameroon in eight environments—varying in seasonal rainfall and temperature patterns and soil characteristics—over two cropping seasons. Soil nutrient content was analyzed and trials were established in a randomized complete block design in three replications. Response of genotypes to major cassava pests and diseases, yield and carotenoids content was evaluated. It was observed that four genotypes did not show cassava mosaic disease (CMD) symptoms irrespective of the environments. The local check had highest CMD incidence and severity across all environments. Average number of whitefly per plant across all environments was highest on TMS 96/0023. Average cassava green mite (CGM) infestation was low on all the genotypes. Fresh root yield of five genotypes ranged between 25 and 30 tons per ha for both years. Significant and positive correlation was found across locations between fresh root yield and soil K, P and Mg. AMMI analysis revealed highly significant differences among genotypes and environments and significant genotype × environment interaction for most of the estimated traits, indicating variability in genotypes performance with environment.

Cassava mosaic disease (CMD) is a major disease affecting cassava production in Southeast Asia. This study aimed to perform an integrated proteomics and metabolomics analysis of cassava cv. Kasetsart 50 infected with Sri Lankan cassava mosaic virus (SLCMV). Proteomics analyses revealed that 359 proteins were enriched in the plant–pathogen interaction, plant hormone signal transduction, and MAPK signaling pathways. A total of 79 compounds were identified by metabolomics analysis of the healthy and SLCMV-infected cassava plants. Integrated omics analysis revealed that 9 proteins and 5 metabolites were enriched in 11 KEGG pathways. The metabolic pathways, plant hormone signal transduction, and plant–pathogen interaction pathway terms were specifically investigated. The findings revealed that caffeic acid and chlorogenic acid were associated with the plant–pathogen interaction pathway, histidine (HK3) was involved in plant hormone signal transduction, while citric acid and D-serine were associated with the metabolic pathways. KEGG functional enrichment analysis revealed that plant–pathogen interaction, plant hormone signal transduction, and metabolic pathways were linked via the enriched protein (protein phosphatase 2C) and metabolites (cyclic nucleotide-binding (AT2G20050) and D-serine). The available information and resources for proteomics and metabolomics analyses of cassava can elucidate the mechanism of disease resistance and aid in cassava crop improvement programs. [ABSTRACT FROM AUTHOR]

Detecting cassava leaf disease is challenging because it is hard to identify diseases accurately through visual inspection. Even trained agricultural experts may struggle to diagnose the disease correctly which leads to potential misjudgements. Traditional methods to diagnose these diseases are time-consuming, prone to error, and require expert knowledge, making automated solutions highly preferred. This paper explores the application of advanced deep learning techniques to detect as well as classify cassava leaf diseases which includes EfficientNet models, DenseNet169, Xception, MobileNetV2, ResNet models, Vgg19, InceptionV3, and InceptionResNetV2. A dataset consisting of around 36,000 labelled images of cassava leaves, afflicted by diseases such as Cassava Brown Streak Disease, Cassava Mosaic Disease, Cassava Green Mottle, Cassava Bacterial Blight, and healthy leaves, was used to train these models. Further the images were pre-processed by converting them into grayscale, reducing noise using Gaussian filter, obtaining the region of interest using Otsu binarization, Distance transformation, as well as Watershed technique followed by employing contour-based feature selection to enhance model performance. Models, after fine-tuned with ADAM optimizer computed that among the tested models, the hybrid model (DenseNet169 + EfficientNetB0) had superior performance with classification accuracy of 89.94% while as EfficientNetB0 had the highest values of precision, recall, and F1score with 0.78 each. The novelty of the hybrid model lies in its ability to combine DenseNet169's feature reuse capability with EfficientNetB0's computational efficiency, resulting in improved accuracy and scalability. These results highlight the potential of deep learning for accurate and scalable cassava leaf disease diagnosis, laying the foundation for automated plant disease monitoring systems., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Cassava is the staple food crop for hundreds of millions of people in Africa. In Côte d'Ivoire, it is a main source of calories for over 26 million people. However, cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses (CMGs) threaten its production. The development, adoption, and use of CMD resistant varieties remain a key CMD management strategy. Therefore, 610 accessions from the Côte d'Ivoire national cassava germplasm maintained by Centre National de Recherche Agronomique (CNRA) research stations in the cities of Man and Bouaké were characterized to assess their resistance to CMD. We found 72 accessions which were symptomless at both sites. Thirty five out of these 72 accessions were infected by African cassava mosaic virus (ACMV) without any CMD symptoms and 37 were virus free. None of the 72 symptomless accessions were infected by East African cassava mosaic Cameroon virus (EACMCMV). The remaining 538 accessions were CMD infected and displayed clear CMD symptoms. The promising 72 accessions (10 locals and 62 improved) were then tested for the presence of resistance genes, CMD1, CMD2 or CMD3. Except for 2 accessions for which no resistance gene was found, the remaining 70 accessions contained one or more resistance genes. Genotyping of the 69 symptomless accessions revealed that 56 were unique genotypes and 13 were potential duplicates. Accessions were structured in three groups with the variabilities at the individual's level. These findings reveal the existence of potential tolerant/resistant cassava accessions in CNRA's germplasm, which can contribute to CMD control and the increase of cassava production in Côte d'Ivoire.

Eighty-five plant species growing near cassava fields were collected and tested by PCR for the presence of begomoviruses and AC1 and AV1 gene of Sri Lankan cassava mosaic virus (SLCMV). This survey revealed that three Euphorbiaceae species, Cnidoscolus chayamansa, Jatropha curcas, and J. multifida, were infected by SLCMV and had mosaic, yellowing, and leaf curling, similar to the symptoms observed on cassava. DNA from the three plant species was analyzed using rolling circle amplification, then Illumina sequencing; the sequences obtained by de novo assembly had high similarity with those of SLCMV of cassava from Southeast Asia. [ABSTRACT FROM AUTHOR]

Simple Summary: The whitefly species Bemisia tabaci is a known pest of cassava and a vector of cassava geminiviruses in Africa and India, but its role in the recent spread of Cassava Mosaic Disease (CMD) in Southeast Asia is not well known. This is in part due to a lack of data on the occurrence and distribution of B. tabaci in this region. We show here the first results of any country-wide survey and identification of B. tabaci colonizing cassava in Lao PDR. Cassava Mosaic Disease (CMD) caused by Sri Lankan cassava mosaic virus (SLCMV), has rapidly spread in Southeast Asia (SEA) since 2016. Recently it has been documented in Lao PDR. Previous reports have identified whitefly species of B. tabaci as potential vectors of CMD in SEA, but their occurrence and distribution in cassava fields is not well known. We conducted a countrywide survey in Lao PDR for adult whiteflies in cassava fields, and determined the abundance and genetic diversity of the B. tabaci species complex using mitochondrial cytochrome oxidase I (mtCOI) sequencing. In order to expedite the process, PCR amplifications were performed directly on whitefly adults without DNA extraction, and mtCOI sequences obtained using nanopore portable-sequencing technology. Low whitefly abundances and two cryptic species of the B. tabaci complex, Asia II 1 and Asia II 6, were identified. This is the first work on abundance and genetic identification of whiteflies associated with cassava in Lao PDR. This study indicates currently only a secondary role for Asia II in spreading CMD or as a pest. Routine monitoring and transmission studies on Asia II 6 should be carried out to establish its potential role as a vector of SLCMV in this region. [ABSTRACT FROM AUTHOR]

Cassava (Manihot esculenta Crantz) is an important root crop in the Philippines. Worldwide, it is attacked by various disease-causing fungi, bacteria, nematodes, and viruses, negatively affecting its yield potential. However, in the Philippines, no viral disease in cassava has yet been scientifically reported. In other cassava growing regions, the three economically important cassava virus diseases, worldwide, are cassava mosaic disease, cassava brown streak disease, and cassava frogskin disease. These three diseases, and their associated viruses, have not been detected in the country. Other viruses are also associated with cassava but their symptomatology and characteristics are yet to be elucidated. Cassava viruses can be disseminated through infected stem propagules and transmitted effectively by whitefly (Bemisia tabaci). The exchange of planting materials, migratory behavior of insect vectors, and current disease distribution can put the country at high risk of a possible virus disease outbreak that can threaten the cassava industry. Eradication is difficult once the disease has been established in the field, which means stricter border control measures are needed. This paper reviews the current knowledge of cassava virus diseases not yet reported in the Philippines but have biosecurity importance. The paper highlights measures that can help prevent, prepare for, and respond to cassava viruses' possible incursion. Given the potential threats, the country should remain vigilant to these cassava virus diseases. [ABSTRACT FROM AUTHOR]

Cassava mosaic disease (CMD), caused by Sri Lankan cassava mosaic virus (SLCMV), was first detected in Tay Ninh province in the southeast region of Vietnam in 2017 and is an emerging threat for cassava production in Vietnam. This study was conducted to characterize the causal agent of CMD in Nghe An province in the north-central region of Vietnam, which is more than 1,200 km away from Tay Ninh province. Genetic relationships between SLCMV isolates indicated that both DNA-A and DNA-B sequences from Nghe An province were identical with the isolates from Tay Ninh province and were highly homologous (>99.7%) with isolates from Cambodia, Thailand and China. This study confirms the gradual spread of SLCMV in Vietnam as an emerging threat to cassava production. In addition, the outcome of this study could help in the timely enforcement of effective management strategies for the cassava mosaic disease in Vietnam. [ABSTRACT FROM AUTHOR]

Abstract Background Cassava is a staple food for over 800 million people globally providing a cheap source of carbohydrate. However, the cultivation of cassava in the country is facing to viral diseases, particularly cassava mosaic disease (CMD) which can cause up to 95% yield losses. With aim to supply farmers demand for clean planting materials, there is need to accelerate the production of the elite cultivars by use of tissue culture in order to cope with the demand. Methods Nodal explants harvested from the greenhouse grown plants were sterilised using different concentrations of a commercial bleach JIK (3.85% NaOCl) and varying time intervals. Microshoots induction was evaluated using thidiazuron (TDZ), benzyl amino purine (BAP), and kinetin. Rooting was evaluated using different auxins (Naphthalene acetic acid NAA and Indole-3-butyricacid IBA). PCR-based SSR and SCAR markers were used to verify the presence of CMD2 gene in the regenerated plantlets. Results The highest level of sterility in explants (90%) was obtained when 20% Jik was used for 15 min. The best cytokinin for microshoots regeneration was found to be kinetin with optimum concentrations of 5, 10 and 20 μM for Agric-rouge, Atinwewe, and Agblehoundo respectively. Medium without growth regulators was the best for rooting the three cultivars. A survival rate of 100, 98, and 98% was recorded in the greenhouse for Agric-rouge, Atinwewe, and Agblehoundo respectively and the plantlets appeared to be morphologically normal. The SSR and SCAR analysis of micropropagated plants showed a profile similar to that of the mother plants indicating that the regenerated plantlets retained the CMD2 gene after passing through in vitro culture, as expected with micropropagation. Conclusion The nodal explants was established to be 20% of Jik (3.85% NaOCl) with an exposure time of 15 min. Kinetin was proved to be the best cytokinins for microshoot formation with the optimum concentration of 5, 10 and 20 μM for Agric-rouge, Atinwewe, and Agblehoundo respectively. The protocol developed during this study will be useful for mass propagation of the elite cassava cultivars.

Cassava Mosaic Disease (CMD) is the prominent cassava disease which compromises cassava production in Africa, both qualitatively and quantitatively for many years. In this study, the mathematical model for the dynamics of CMD with Non-cassava host plant population is formulated and analysed. The analysis of basic model properties confirmed the positive boundedness of the model solution for all time t≥0. Utilizing the next generation matrix the basic reproduction number R0 is derived and stability of disease-free equilibrium point (DFE) is analysed. Analytical results confirmed that, the disease-free equilibrium point (DFE) is locally asymptotically stable whenever R0

In this investigation, we formulate and analyse a stochastic epidemic model using the continuous-time Markov chain model for the propagation of a vector-borne cassava mosaic disease in a single population. The stochastic model is based upon a pre-existing deterministic plant-vector-virus model. To see how demographic stochasticity affects the vector-borne cassava mosaic disease dynamics, we compare the disease dynamics of both deterministic and stochastic models through disease extinction process. The probability of disease extinction and therefore the major outbreak are estimated analytically using the multitype Galton–Watson branching process (GWbp) approximation. Also, we have found the approximate probabilities of disease extinction numerically based on 30000 sample paths, and it is shown to be good estimate with the calculated probabilities from GWbp approximation. In particular, it is observed that there is a very high probability of disease extinction when the disease is introduced via the infected vectors rather than through infected plants. [ABSTRACT FROM AUTHOR]

Cassava is a vital food-security crop in Sub-Saharan Africa. Cassava crops are, however, severely affected by viral diseases transmitted by members of the whitefly species complex Bemisia tabaci. We have here investigated the role of olfaction in host selection behavior of the cassava whitefly B. tabaci SSA-ESA biotype. Surprisingly, we find that the whiteflies appear to make little use of olfaction to find their favored host. The cassava whitely shows a highly reduced olfactory system, both at the morphological and molecular level. Whitefly antennae possess only 15 sensilla with possible olfactory function, and from the genome we identified just a handful of candidate chemoreceptors, including nine tuning odorant receptors, which would afford the whitefly with one of the smallest olfactomes identified from any insect to date. Behavioral experiments with host and non-host plants, as well as with identified specific volatiles from these sources, suggest that the few input channels present are primarily tuned toward the identification of unwanted features, rather than favored ones, a strategy quite unlike most other insects. The demonstrated repellence effect of specific volatile chemicals produced by certain plants unflavored by whiteflies suggests that intercropping with these plants could be a viable strategy to reduce whitefly infestations in cassava fields.

The dataset presented here was collected during field surveys conducted in 2015 and 2017, to determine the distribution of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) across 12 Nigerian states and the Federal Capital Territory (FCT), Abuja. In each state, cassava farms were systematically sampled at 10 km intervals except in locations with sparse distribution of cassava farms. In each farm, 30 cassava plants were visually assessed for presence or absence of cassava mosaic disease (CMD) foliar symptoms along two diagonals. Whitefly population was assessed by counting the number of whiteflies on the top five leaves of each sampled plant. Then an average of 4 cassava leaf samples were collected from each farm, and screened for ACMV and EACMV infections using polymerase chain reaction. The dataset includes CMD incidence, symptom severity and the relative abundance of whiteflies in each field as well as laboratory results that show the distribution of ACMV and EACMV across the regions surveyed.

Cassava mosaic disease caused by cassava mosaic begomoviruses (CMBs) remains one of the major constraints to cassava production since it causes yield losses up to 100%. Researches showed that some of CMBs infecting cassava plants may be coming from non-crop plants. This study intended to identify and characterize CMBs isolated from non-crop plant species in Unguja and Pemba Islands. A total of 108 viral symptomatic and asymptomatic non-crop leaf samples were collected using stratified sampling. DNA was extracted by using CTAB protocol followed by polymerase chain reaction using universal and specific primers for cassava mosaic begomoviruses identification. Results showed that, among eleven samples that were amplified, four were African cassava mosaic viruses (ACMV) and seven were East African cassava mosaic viruses (EACMV). DNA sequencing by Sanger method showed 97-99% similarities with isolates of ACMV and EACMV reported elsewhere in Africa. Using RbcL and MatK plant barcode genes, Datura stramonium, Solanum melongena and Solanum incanum were found associated with ACMV, while Senna occidentalis, Sida acuta and Ricinus communis harboured EACMV. These findings are a key in understanding the epidemiology of cassava mosaic disease and are potential in the development of sustainable management strategies for this disease. [ABSTRACT FROM AUTHOR]

Cassava (Manihot esculenta) is an important food crop across sub-Saharan Africa, where production is severely inhibited by two viral diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), both propagated by a whitefly vector and via human-mediated movement of infected cassava stems. There is limited information on growers' behavior related to movement of planting material, as well as growers' perception and awareness of cassava diseases, despite the importance of these factors for disease control. This study surveyed a total of 96 cassava subsistence growers and their fields across five provinces in Zambia between 2015 and 2017 to address these knowledge gaps. CMD symptoms were observed in 81.6% of the fields, with an average incidence of 52% across the infected fields. No CBSD symptoms were observed. Most growers used planting materials from their own (94%) or nearby (<10 km) fields of family and friends, although several large transactions over longer distances (10 to 350 km) occurred with friends (15 transactions), markets (1), middlemen (5), and nongovernmental organizations (6). Information related to cassava diseases and certified clean (diseasefree) seed reached only 48% of growers. The most frequent sources of information related to cassava diseases included nearby friends, family, and neighbors, while extension workers were the most highly preferred source of information. These data provide a benchmark on which to plan management approaches to controlling CMD and CBSD, which should include clean propagation material, increasing growers' awareness of the diseases, and increasing information provided to farmers (specifically disease symptom recognition and disease management options). [ABSTRACT FROM AUTHOR]

Cassava mosaic disease (CMD), which is caused by singlestranded DNA begomoviruses, severely limits cassava production across Africa. A previous study showed that CMD symptom severity and viral DNA accumulation increase in cassava in the presence of a DNA sequence designated SEGS-2 (sequence enhancing geminivirus symptoms). We report here that when SEGS-2 is coinoculated with African cassava mosaic virus (ACMV) onto Arabidopsis thaliana, viral symptoms increase. Transgenic Arabidopsis with an integrated copy of SEGS-2 inoculated with ACMV also display increased symptom severity and viral DNA levels. Moreover, SEGS-2 enables Cabbage leaf curl virus (CaLCuV) to infect a geminivirus-resistant Arabidopsis thaliana accession. Although SEGS-2 is related to cassava genomic sequences, an earlier study showed that it occurs as episomes and is packaged into virions in CMD-infected cassava and viruliferous whiteflies. We identified SEGS-2 episomes in SEGS-2 transgenic Arabidopsis. The episomes occur as both double-stranded and single-stranded DNA, with the singlestranded form packaged into virions. In addition, SEGS-2 episomes replicate in tobacco protoplasts in the presence, but not the absence, of ACMV DNA-A. SEGS-2 episomes contain a SEGS-2 derived promoter and an open reading frame with the potential to encode a 75-amino acid protein. An ATG mutation at the beginning of the SEGS-2 coding region does not enhance ACMV infection in A. thaliana. Together, the results established that SEGS-2 is a new type of begomovirus satellite that enhances viral disease through the action of an SEGS-2-encoded protein that may also be encoded by the cassava genome. IMPORTANCE Cassava is an important root crop in the developing world and a food and income crop for more than 300 million African farmers. Cassava is rising in global importance and trade as the demands for biofuels and commercial starch increase. More than half of the world's cassava is produced in Africa, where it is primarily grown by smallholder farmers, many of whom are from the poorest villages. Although cassava can grow under high temperature, drought, and poor soil conditions, its production is severely limited by viral diseases. Cassava mosaic disease (CMD) is one of the most important viral diseases of cassava and can cause up to 100% yield losses. We provide evidence that SEGS-2, which was originally isolated from cassava crops displaying severe and atypical CMD symptoms in Tanzanian fields, is a novel begomovirus satellite that can compromise the development of durable CMD resistance. [ABSTRACT FROM AUTHOR]

Abstract Background Cassava is an important food crop in tropical and sub-tropical regions worldwide. In Africa, cassava production is widely affected by cassava mosaic disease (CMD), which is caused by the African cassava mosaic geminivirus that is transmitted by whiteflies. Cassava breeders often use a single locus, CMD2, for introducing CMD resistance into susceptible cultivars. The CMD2 locus has been genetically mapped to a 10-Mbp region, but its organization and genes as well as their functions are unknown. Results We report haplotype-resolved de novo assemblies and annotations of the genomes for the African cassava cultivar TME (tropical Manihot esculenta), which is the origin of CMD2, and the CMD-susceptible cultivar 60444. The assemblies provide phased haplotype information for over 80% of the genomes. Haplotype comparison identified novel features previously hidden in collapsed and fragmented cassava genomes, including thousands of allelic variants, inter-haplotype diversity in coding regions, and patterns of diversification through allele-specific expression. Reconstruction of the CMD2 locus revealed a highly complex region with nearly identical gene sets but limited microsynteny between the two cultivars. Conclusions The genome maps of the CMD2 locus in both 60444 and TME3, together with the newly annotated genes, will help the identification of the causal genetic basis of CMD2 resistance to geminiviruses. Our de novo cassava genome assemblies will also facilitate genetic mapping approaches to narrow the large CMD2 region to a few candidate genes for better informed strategies to develop robust geminivirus resistance in susceptible cassava cultivars.

Achieving food security for an ever-increasing human population requires faster development of improved varieties. To this end, assessment of genetic gain for key traits is important to inform breeding processes. Despite the improvements made to increase production and productivity of cassava in Uganda at research level, there has been limited effort to quantify associated genetic gains. Accordingly, a study was conducted in Uganda to assess whether or not genetic improvement was evident in selected cassava traits using cassava varieties that were released from 1940 to 2019. Thirty-two varieties developed during this period, were evaluated simultaneously in three major cassava production zones; central (Namulonge), eastern (Serere), and northern (Loro). Best linear unbiased predictors (BLUPs) of the genotypic value for each clone were obtained across environments and regressed on order of release year to estimate annual genetic gains. We observed that genetic trends were mostly quadratic. On average, cassava mosaic disease (CMD) resistance increased by 1.9% per year, while annual genetic improvements in harvest index (0.0%) and fresh root yield (−5 kg per ha or −0.03% per ha) were non-substantial. For cassava brown streak disease (CBSD) resistance breeding which was only initiated in 2003, average annual genetic gains for CBSD foliar and CBSD root necrosis resistances were 2.3% and 1.5%, respectively. It’s evident that cassava breeding has largely focused on protecting yield against diseases. This underpins the need for simultaneous improvement of cassava for disease resistance and high yield for the crop to meet its current and futuristic demands for food and industry.

Achieving food security for an ever-increasing human population requires faster development of improved varieties. To this end, assessment of genetic gain for key traits is important to inform breeding processes. Despite the improvements made to increase production and productivity of cassava in Uganda at research level, there has been limited effort to quantify associated genetic gains. Accordingly, a study was conducted in Uganda to assess whether or not genetic improvement was evident in selected cassava traits using cassava varieties that were released from 1940 to 2019. Thirty-two varieties developed during this period, were evaluated simultaneously in three major cassava production zones; central (Namulonge), eastern (Serere), and northern (Loro). Best linear unbiased predictors (BLUPs) of the genotypic value for each clone were obtained across environments and regressed on order of release year to estimate annual genetic gains. We observed that genetic trends were mostly quadratic. On average, cassava mosaic disease (CMD) resistance increased by 1.9% per year, while annual genetic improvements in harvest index (0.0%) and fresh root yield (−5 kg per ha or −0.03% per ha) were non-substantial. For cassava brown streak disease (CBSD) resistance breeding which was only initiated in 2003, average annual genetic gains for CBSD foliar and CBSD root necrosis resistances were 2.3% and 1.5%, respectively. It's evident that cassava breeding has largely focused on protecting yield against diseases. This underpins the need for simultaneous improvement of cassava for disease resistance and high yield for the crop to meet its current and futuristic demands for food and industry. [ABSTRACT FROM AUTHOR]

Summary: Delivering the benefits of agricultural biotechnology to smallholder farmers requires that resources be directed towards staple food crops. To achieve effect at scale, beneficial traits must be integrated into multiple, elite farmer‐preferred varieties with relevance across geographical regions. The staple root crop cassava (Manihot esculenta) is consumed for dietary calories by more than 800 million people, but its tuberous roots provide insufficient iron and zinc to meet nutritional needs. In Africa, cassava yields are furthermore limited by the virus diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). In this study, we strove to develop cassava displaying high‐level resistance to CBSD and CMD to attain food and economic security for cassava farmers, along with biofortified levels of iron and zinc to enhance consumer health. RNAi‐mediated technology was used to achieve resistance to CBSD in two East African and one Nigerian farmer‐preferred cultivars that harboured resistance to CMD. The Nigerian cvs. TMS 95/0505 and TMS 91/02324 were modified with T‐DNA imparting resistance to CBSD, along with AtIRT1 (major iron transporter) and AtFER1 (ferritin) transgenes to achieve nutritionally significant levels of iron and zinc in cassava storage roots (145 and 40 µg/g dry weight, respectively). The inherent resistance to CMD was maintained in all four disease resistant and mineral enhanced cassava cultivars described here, demonstrating that this technique could be deployed across multiple farmer‐preferred varieties to benefit the food and nutritional security of consumers in Africa. [ABSTRACT FROM AUTHOR]

Cassava mosaic disease (CMD), arguably the most important viral disease of cassava, an important food security crop has in recent times, been reported to be associated with satellites in some parts of sub-Saharan Africa. We investigated the status of Cassava mosaic begomovirus and associated satellites in CMD-affected cassava plants in Ghana using polymerase chain reaction. In all, 110 CMD-affected cassava leaf samples collected from cassava fields in Southern Ghana. Africa cassava mosaic virus (ACMV) was detected in 107 (97%) cassava leaf samples, out of which 76 (69%) was in mixed infections with East Africa cassava mosaic virus-Cameroon (EACMV-CM). EACMV (CM) alone was detected in three (3%) cassava leaf samples. Out of the 110 cassava leaf samples affected by cassava mosaic begomoviruses, satIII and satII were detected in 66 (60%) and 47 (43%), respectively. To the best of our knowledge, detection of CMB-associated satellites in Ghana is the first in the country and possibly in West Africa, and has serious epidemiological implications on the management of CMD, thereby requiring further studies and concerted efforts to safeguard cassava production.

Nuru is a deep learning object detection model for diagnosing plant diseases and pests developed as a public good by PlantVillage (Penn State University), FAO, IITA, CIMMYT, and others. It provides a simple, inexpensive and robust means of conducting in-field diagnosis without requiring an internet connection. Diagnostic tools that do not require the internet are critical for rural settings, especially in Africa where internet penetration is very low. An investigation was conducted in East Africa to evaluate the effectiveness of Nuru as a diagnostic tool by comparing the ability of Nuru, cassava experts (researchers trained on cassava pests and diseases), agricultural extension officers and farmers to correctly identify symptoms of cassava mosaic disease (CMD), cassava brown streak disease (CBSD) and the damage caused by cassava green mites (CGM). The diagnosis capability of Nuru and that of the assessed individuals was determined by inspecting cassava plants and by using the cassava symptom recognition assessment tool (CaSRAT) to score images of cassava leaves, based on the symptoms present. Nuru could diagnose symptoms of cassava diseases at a higher accuracy (65% in 2020) than the agricultural extension agents (40–58%) and farmers (18–31%). Nuru’s accuracy in diagnosing cassava disease and pest symptoms, in the field, was enhanced significantly by increasing the number of leaves assessed to six leaves per plant (74–88%). Two weeks of Nuru practical use provided a slight increase in the diagnostic skill of extension workers, suggesting that a longer duration of field experience with Nuru might result in significant improvements. Overall, these findings suggest that Nuru can be an effective tool for in-field diagnosis of cassava diseases and has the potential to be a quick and cost-effective means of disseminating knowledge from researchers to agricultural extension agents and farmers, particularly on the identification of disease symptoms and their management practices.

Abstract Background Morphogenic culture systems are central to crop improvement programs that utilize transgenic and genome editing technologies. We previously reported that CMD2-type cassava (Manihot esculenta) cultivars lose resistance to cassava mosaic disease (CMD) when passed through somatic embryogenesis. As a result, these plants cannot be developed as products for deployment where CMD is endemic such as sub-Saharan Africa or the Indian sub-continent. Result In order to increase understanding of this phenomenon, 21 African cassava cultivars were screened for resistance to CMD after regeneration through somatic embryogenesis. Fifteen cultivars were shown to retain resistance to CMD through somatic embryogenesis, confirming that the existing transformation and gene editing systems can be employed in these genetic backgrounds without compromising resistance to geminivirus infection. CMD2-type cultivars were also subjected to plant regeneration via caulogenesis and meristem tip culture, resulting in 25–36% and 5–10% of regenerated plant lines losing resistance to CMD respectively. Conclusions This study provides clear evidence that multiple morphogenic systems can result in loss of resistance to CMD, and that somatic embryogenesis per se is not the underlying cause of this phenomenon. The information described here is critical for interpreting genomic, transcriptomic and epigenomic datasets aimed at understanding CMD resistance mechanisms in cassava.