East African cassava mosaic virus. [Distribution map].

A new distribution map is provided for East African cassava mosaic virus (Geplafuvirales: Geminiviridae: Begomovirus). Host: cassava (Manihot esculenta). Information is given on the geographical distribution in Africa (Angola, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Comoros, Democratic Republic of the Congo, Equatorial Guinea, Eswatini, Gabon, Ghana, Guinea, Ivory Coast, Kenya, Madagascar, Malawi, Mayotte, Mozambique, Nigeria, Republic of the Congo, Rwanda, Seychelles, Sierra Leone, South Africa, Sudan, Tanzania, Zanzibar, Togo, Uganda and Zambia).

Proteome Mapping of South African Cassava Mosaic Virus-Infected Susceptible and Tolerant Landraces of Cassava

The production of cassava is threatened by the geminivirus South African cassava mosaic virus (SACMV), which causes cassava mosaic disease. Cassava landrace TME3 shows tolerance to SACMV, while T200 is highly susceptible. This study aimed to identify the leaf proteome involved in anti-viral defence. Liquid chromatography mass spectrometry (LC-MS) identified 2682 (54 differentially expressed) and 2817 (206 differentially expressed) proteins in both landraces at systemic infection (32 days post infection) and symptom recovery (67 days post infection), respectively. Differences in the number of differentially expressed proteins (DEPs) between the two landraces were observed. Gene ontology analysis showed that defence-associated pathways such as the chloroplast, proteasome, and ribosome were overrepresented at 67 days post infection (dpi) in SACMV-tolerant TME3. At 67 dpi, a high percentage (56%) of over-expressed proteins were localized in the chloroplast in TME3 compared to T200 (31% under-expressed), proposing that chloroplast proteins play a role in tolerance in TME3. Ribosomal_L7Ae domain-containing protein (Manes.12G139100) was over-expressed uniquely in TME3 at 67 dpi and interacts with the ribosomal protein Sac52 (RPL10). RPL10 is a known key player in the NIK1-mediated effector triggered immunity (ETI) response to geminivirus infection, indicating a possible role for Sac52 in SACMV recovery in TME3. In conclusion, differential protein expression responses in TME3 and T200 may be key to unravel tolerance to CMD.

Survey and molecular detection of Sri Lankan cassava mosaic virus in Thailand

Cassava plantations in an area of 458 hectares spanning five provinces along the Thailand–Cambodia border were surveyed from October 2018 to July 2019 to determine the prevalence of cassava mosaic disease (CMD) caused by Sri Lankan cassava mosaic virus (SLCMV) in the region. CMD prevalence was 40% in the whole area and 80% in Prachinburi, 43% in Sakaeo, 37% in Burium, 25% in Surin, and 19% in Sisaket provinces. Disease incidence of CMD was highest 43.08% in Sakaeo, followed by 26.78% in Prachinburi, 7% in Burium, 2.58% in Surin, and 1.25% in Sisaket provinces. Disease severity of CMD symptoms was mild chlorosis to moderate mosaic (2–3). The greatest disease severity was recorded in Prachinburi and Sakaeo provinces. Asymptomatic plants were identified in Surin (12%), Prachinburi (5%), Sakaeo (0.2%), and Buriram (0.1%) by PCR analysis. Cassava cultivars CMR-89 and Huai Bong 80 were susceptible to CMD. In 95% of cases, the infection was transmitted by whiteflies (Bemisia tabaci), which were abundant in Sakaeo, Buriram, and Prachinburi but were sparse in Surin; their densities were highest in May and June 2019. Nucleotide sequencing of the mitochondrial cytochrome oxidase 1 (mtCO1) gene of whiteflies in Thailand revealed that it was similar to the mtCO1 gene of Asia II 1 whitefly. Furthermore, the AV1 gene of SLCMV—which encodes the capsid protein—showed 90% nucleotide identity with SLCMV. Phylogenetic analysis of completed nucleotide sequences of DNA-A and DNA-B components of the SLCMV genome determined by rolling circle amplification (RCA) indicated that they were similar to the nucleotide sequence of SLCMV isolates from Thailand, Vietnam, and Cambodia. These results provide important insights into the distribution, impact, and spread of CMD and SLCMV in Thailand.

East African cassava mosaic virus.

Like other CMGs, cassava is the primary host of East African cassava mosaic virus (EACMV) and related viruses, although the virus has been detected in other plant species (Ogbe et al., 2006; Alabi et al. 2015). Analysis of the genomes of different isolates of EACMV-type viruses show considerable genetic variability and genome plasticity relative to ACMV isolates. The primary means of virus spread is via movement of contaminated vegetative cassava cuttings and secondary spread occurs via the whitefly vector, Bemisia tabaci. Perhaps the most notable documentation of invasiveness of EACMV-type viruses is the regional pandemic of a severe CMD in East Africa caused by EACMV-UG which began in Uganda in the early to mid-1990s (Gibson et al., 1996; Otim-Nape et al., 1997) on popular and widely cultivated cassava varieties and soon spread to other countries in East Africa, including Kenya and Tanzania (Otim-Nape et al., 1997; Legg, 1999). The pandemic resulted in famine-related deaths (Otim-Nape et al., 1998) due to complete devastation of affected cassava farms in the region. EACMV is not on the IUCN or ISSG alert list.

Survey and Molecular Detection of Sri Lankan Cassava Mosaic Virus in Thailand

Cassava plantations in an area of 458 ha spanning five provinces along the Thailand–Cambodia border were surveyed from October 2018 to July 2019 to determine the prevalence of cassava mosaic disease (CMD) caused by Sri Lankan cassava mosaic virus (SLCMV) in the region. CMD prevalence was 40% in the whole area and 80% in Prachinburi, 43% in Sakaeo, 37% in Burium, 25% in Surin, and 19% in Sisaket provinces. Disease severity was generally scored as 2–3. The highest average disease severity was in Sakaeo province (3.7), followed by Buriram (3.6), Prachinburi (2.88), Surin (2.5), and Sisaket (2.4) provinces. Asymptomatic plants were identified in Surin (12%), Prachinburi (5%), Sakaeo (0.2%), and Buriram (0.1%) by PCR analysis. Interestingly, cassava cultivars CMR-89 and Rayong 11 were susceptible to CMD. In approximately 95% of cases, the infection was transmitted by whitefly ( Bemisia tabaci ), which had a high population density in Prachinburi but was sparse in Surin, with the largest populations observed in May and June. Nucleotide sequencing of the mitochondrial cytochrome oxidase 1 ( mtCO1 ) gene of whitefly ( Bemisia tabaci ) in Thailand revealed a similarity to the Asia II 1 whitefly gene. Furthermore, the AV1 gene—which encodes the capsid protein—showed 90% nucleotide identity with SLCMV. Phylogenetic analysis of completed nucleotide sequences of DNA-A and DNA-B components of the SLCMV genome determined by rolling circle amplification (RCA) indicated that they were similar to the nucleotide sequence of SLCMV isolates from Thailand, Vietnam, and Cambodia. These results provide important insights into the distribution, impact, and spread of CMD and SLCMV in Thailand.

Development of a triple antibody sandwich enzyme-linked immunosorbent assay for cassava mosaic disease detection using a monoclonal antibody to Sri Lankan cassava mosaic virus

Background Cassava mosaic disease (CMD) is one of the most devastating viral diseases for cassava production in Africa and Asia. Accurate yet affordable diagnostics are one of the fundamental tools supporting successful CMD management, especially in developing countries. This study aimed to develop an antibody-based immunoassay for the detection of Sri Lankan cassava mosaic virus (SLCMV), the only cassava mosaic begomovirus currently causing CMD outbreaks in Southeast Asia (SEA). Methods Monoclonal antibodies (MAbs) against the recombinant coat protein of SLCMV were generated using hybridoma technology. MAbs were characterized and used to develop a triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) for SLCMV detection in cassava leaves and stems. Assay specificity, sensitivity and efficiency for SLCMV detection was investigated and compared to those of a commercial ELISA test kit and PCR, the gold standard. Results A TAS-ELISA for SLCMV detection was successfully developed using the newly established MAb 29B3 and an in-house polyclonal antibody (PAb) against begomoviruses, PAb PK. The assay was able to detect SLCMV in leaves, green bark from cassava stem tips, and young leaf sprouts from stem cuttings of SLCMV-infected cassava plants without cross-reactivity to those derived from healthy cassava controls. Sensitivity comparison using serial dilutions of SLCMV-infected cassava sap extracts revealed that the assay was 256-fold more sensitive than a commercial TAS-ELISA kit and 64-fold less sensitive than PCR using previously published SLCMV-specific primers. In terms of DNA content, our assay demonstrated a limit of detection of 2.21 to 4.08 × 106 virus copies as determined by quantitative real-time PCR (qPCR). When applied to field samples (n = 490), the TAS-ELISA showed high accuracy (99.6%), specificity (100%), and sensitivity (98.2%) relative to the results obtained by the reference PCR. SLCMV infecting chaya (Cnidoscolus aconitifolius) and coral plant (Jatropha multifida) was also reported for the first time in SEA. Conclusions Our findings suggest that the TAS-ELISA for SLCMV detection developed in this study can serve as an attractive tool for efficient, inexpensive and high-throughput detection of SLCMV and can be applied to CMD screening of cassava stem cuttings, large-scale surveillance, and screening for resistance.

African cassava mosaic virus (African cassava mosaic).

Cassava is vegetatively propagated therefore ACMV and other CMGs are primarily transmitted via movement of contaminated cuttings. Consequently, introductions of specific CMGs into new localities mirror patterns of cassava cuttings exchange among farmers. Once infected cuttings are planted, the virus establishes easily and can be transmitted within and between fields through the feeding behaviour of the whitefly vector, Bemisia tabaci. ACMV is particularly invasive in that it is the most widespread of all known CMGs, occurring across all cassava-producing countries of Africa in cassava and several alternative host plants (Thottappilly et al., 2003; Alabi et al. 2015). ACMV has also been reported infecting non-cultivated exotic cotton species in Pakistan (Nawaz-Ul-Rehman et al., 2012) further underscoring its invasive nature. Yield loss due to CMD can range from 12 to 82%, depending on the cassava variety and infection type (Owor et al., 2004). ACMV is not on the IUCN or ISSG alert list.

Indian cassava mosaic virus (Indian cassava mosaic).

Other than their countries of origin, India and Sri Lanka for ICMV and SLCMV, respectively, SLCMV has also been reported in India (Dutt et al., 2005; Jose et al., 2011) and Cambodia (Wang et al., 2016) while new strains of ICMV have been identified as causative agents of Jatropha curcas mosaic disease in Jatropha curcas from India (Snehi et al., 2012), Nigeria (Kashina et al., 2013) and Singapore (Wang et al., 2014). The primary means of spread of both viruses is via movement of infected cassava cuttings while secondary spread is facilitated by members of the Bemisia tabaci complex. Both ICMV and SLCMV are not on the IUCN or ISSG alert lis.