Preferred Scientific Name
- East African cassava mosaic virus
International Common Names
- Spanish: Mosaico africano de la yuca
- French: Mosaïque africaine du manioc
English acronym
- EACMV
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Generate reportLike 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.
East African cassava mosaic virus (EACMV) is a member of the genus Begomovirus (family Geminiviridae). Like the African cassava mosaic virus (ACMV), EACMV is a ssDNA virus, transmitted by whiteflies (Bemisia tabaci) with cassava as its primary host plant. Initially considered to be a strain of ACMV (Bock and Harrison, 1985), evidence for its distinctness as a species came by way of nucleotide sequence (Hong et al., 1993) and serological (Swanson and Harrison, 1994) data. Since then, five other molecularly distinct but serologically related EACMV-type viruses have been characterized from cassava mosaic disease (CMD) affected vine: East African cassava mosaic Malawi virus (EACMMV), East African cassava mosaic Cameroon virus (EACMCV), East African cassava mosaic Zanzibar virus (EACMZV), East African cassava mosaic Kenya virus (EACMKV) and Cassava mosaic Madagascar virus (CMMGV). A severe form of EACMV known as EACMV-Ugandan variant (EACMV-UG) has been reported from several sub-Saharan African countries and linked to severe CMD epidemics in Eastern African countries (Otim-Nape et al., 1997; Harrison et al., 1997; Karakacha et al., 2001; Legg et al., 2001; Neuenschwander et al., 2002; Birigimana et al., 2004; Legg et al., 20004; Ntawuruhunga et al., 2007; Kumar et al., 2008; Akinbade et al., 2010). In a recent revision of the Begomovirus taxonomy by the ICTV Geminiviridae subgroup, EACMCV was downgraded to the status of a strain of EACMV (Brown et al., 2015).
EACMV-type viruses possess bipartite, circular, ss(+)DNA genomes that are encapsidated in twin (geminate), small, quasi-isometric particles measuring 20 x 30 nm. Both the DNA-A and DNA-B genome components are needed for efficient transmission of the virus to healthy cassava plants (Liu et al., 1997). Whereas this description is used sensu lato, there is considerable variability among EACMV-type viruses at the molecular level. Each species is named after its country of first discovery/characterization although the use of country names in geminivirus nomenclature is now being discouraged (Brown et al., 2015).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Last updated: 21 Jul 2022Continent/Country/Region | Distribution | Last Reported | Origin | First Reported | Invasive | Reference | Notes |
---|---|---|---|---|---|---|---|
Africa |
|||||||
Angola | Present | Native | 2009 | Invasive | |||
Burkina Faso | Present | ||||||
Burundi | Present, Widespread | Native | Invasive | ||||
Cameroon | Present, Widespread | Native | Invasive | ||||
Central African Republic | Present | Introduced | Invasive | ||||
Chad | Present | Native | Invasive | ||||
Comoros | Present | Introduced | Invasive | ||||
Congo, Democratic Republic of the | Present | ||||||
Congo, Republic of the | Present, Widespread | Native | Invasive | ||||
Côte d'Ivoire | Present | Introduced | Invasive | ||||
Equatorial Guinea | Present | ||||||
Eswatini | Present | ||||||
Gabon | Present | Native | Invasive | ||||
Ghana | Present | Native | Invasive | ||||
Guinea | Present, Few occurrences | Only a few samples of EACMV were found. | |||||
Kenya | Present | Invasive | |||||
Madagascar | Present, Widespread | Native | Invasive | Prevalent in lowlands and coastal regions. | |||
Malawi | Present | ||||||
Mayotte | Present | Introduced | Invasive | ||||
Mozambique | Present | Invasive | |||||
Nigeria | Present | Invasive | |||||
Rwanda | Present, Widespread | Native | Invasive | ||||
Seychelles | Present | Introduced | Invasive | ||||
Sierra Leone | Present | ||||||
South Africa | Present | Native | Invasive | ||||
Sudan | Present | ||||||
Tanzania | Present, Widespread | Native | Invasive | ||||
-Zanzibar Island | Present | Native | Invasive | ||||
Togo | Present | ||||||
Uganda | Present | Native | Invasive | ||||
Zambia | Present, Widespread | Native | Invasive |
EACMV is thought to be native to the African continent and its surrounding islands. Although the primary host, cassava, was introduced to Africa from South America in the sixteenth and eighteenth centuries, EACMV and other CMGs have not been reported in the Americas. Evolutionary studies conducted with virus isolates sampled from mainland Africa and the South West Indian Ocean (SWIO) islands of Comoros and Seychelles archipelagos have revealed that spread of three EACMV-type viruses from from the former to the latter region probably occurred via at least four independent introduction events estimated to have taken place between 1988 and 2009 (De Bruyn et al., 2012). In mainland Africa, EACMV is found in virtually all cassava-growing areas spanning several eastern (Legg, 1999; Ndunguru et al., 2005, 2016; Bull et al., 2006), western (Fauquet and Fargette, 1990; Ogbe et al., 1990; Fondong et al., 1998; Offei et al., 1999) and southern (Mabasa, 2007; Kumar et al., 2009; Cossa, 2011; Chikoti et al. 2013; Mulenga et al., 2016) countries.
There are two major pathways for the introduction of EACMV and other CMGs to new areas, namely through distribution of planting materials and by the naturally transmitting whitefly vector, Bemisia tabaci. Infected cassava vegetative cuttings contribute to both long and short distance spread of EACMV and other CMGs. Whitefly mediated spread generally occurs over short distances because B. tabaci is a ‘weak’ flier with an estimated flight speed of ca 0.2 m/sec (Chant, 1958; Dubern, 1994) unless aided by the prevailing wind. Moreover, for every population of adult whiteflies feeding on infected cassava plants, up to 13% would acquire the virus and become infective (Legg et al., 2011). It would therefore require a huge whitefly population to cause widespread transmission. But the population dynamics of B. tabaci is influenced by many factors including environmental and biological factors and an abundance of susceptible cassava varieties. High populations are therefore highly likely in countries with a biannual rainfall pattern where cassava plants at the right foliar stage for feeding exist continually. In countries where whitefly populations are low, such as Zambia (Chikoti et al., 2013), Malawi (Mbewe et al., 2015) and Mozambique (Cossa, 2011), the pathway supporting introduction of EACMV to other areas is the movement of uncertified planting materials by farmers, NGOs and other stakeholders. Thus, cutting-borne infections probably contribute more to the spread of EACMV and other CMGs to new field and regions. Once introduced, eradication is difficult because of the nature of continuous cassava cropping and the presence of alternative weed or crop plant hosts of CMGs (Ogbe et al., 2006; Alabi et al., 2008; 2015; Monde et al., 2010).
EACMV is widespread across cassava fields in sub-Saharan African countries and adjoining islands.
EACMV, like the other CMGs, is primarily borne in cassava vegetative cuttings. Emerging leaves from such cuttings may manifest CMD symptoms and serve as sources of virus inoculum for secondary spread within and across fields by the whitefly vector. True cassava seeds are not known to carry the virus (Dubern, 1994). Depending on the mode of infection, symptoms appear in the first emerging leaves for cutting and 12-20 days after inoculation by viruliferous whiteflies (Storey and Nichols, 1938) and are usually determined by varietal characteristics.
Plant name | Family | Context | References |
---|---|---|---|
Ageratum conyzoides (billy goat weed) | Asteraceae | Unknown | |
Combretum confertum | Combretaceae | Unknown | |
Euphorbia hirta (garden spurge) | Euphorbiaceae | Unknown | |
Glycine max (soyabean) | Fabaceae | Other | |
Manihot esculenta (cassava) | Euphorbiaceae | Main | |
Manihot glaziovii (ceara rubber) | Euphorbiaceae | Unknown | |
Markhamia lutea (markhamia) | Bignoniaceae | Unknown | |
Senna occidentalis (coffee senna) | Fabaceae | Unknown |
Cassava plants infected by EACMV and other CMGs display diverse foliar symptoms, the type and severity of which are determined by a number of factors. Symptoms include yellow or green mosaic, mottling, and misshapen and twisted leaves that may be reduced in size. Although these symptoms are characteristic of all CMGs, they differ in distribution in fields, from plant to plant, and even on the same plant. In some cases, two branches emerging from the same cassava plant may show varying phenotypes, with one branch being symptomless and the other exhibiting typical CMD symptoms. Symptom severity also varies with variety, environment and infection type. Plants that are infected by mixed CMGs typically express more severe symptoms than those with single infections. For example, plants that are co-infected with ACMV and EACMV-UG show severe foliar symptoms, as observed in the pandemic movement of a severe form of cassava mosaic disease in East Africa (Zhou et al., 1997). In addition, so-called ‘sequences enhancing geminivirus symptoms (SEGS)’ can enhance cassava mosaic symptoms and break CMD resistance when they interact synergistically with CMGs in cassava plants (Ndunguru et al., 2016). Symptoms-based field diagnosis of EACMV and other CMGs is impracticable due to similarities of induced symptoms in infected plants regardless of the causative CMG. Consequently, it is imperative to confirm virus presence using PCR and/or ELISA methods with species-specific oligonucleotides and discriminating antibodies, respectively. PCR diagnosis is the method of choice for confirmation due to the high serological relationship among EACMV-type viruses and the cross reactivity of their antibodies.
Sign | Life Stages | Type |
---|---|---|
Growing point / dwarfing; stunting | ||
Leaves / abnormal colours | ||
Leaves / abnormal forms | ||
Leaves / abnormal patterns | ||
Roots / reduced root system | ||
Whole plant / distortion; rosetting | ||
Whole plant / dwarfing |
EACMV and other EACMV-like CMGs are transmitted via whitefly vectors and by the movement of infected planting material from field to field and across regions. The whitefly Bemisia tabaci has been known as a vector of cassava mosaic geminiviruses (CMGs) since 1936 (Storey and Nichols, 1938). The acquisition of CMGs by B. tabaci may occur at relatively low (up to 13%) efficiency leading to the conclusion that in pandemic spread of the CMGs a superabundant whitefly population is more important than the transmission efficiency of individual insects (Legg et al., 2010). Observed rates and patterns of CMGs spread is therefore a factor of whitefly abundance and seasonal population dynamics (Alabi et al., 2015, and references therein). Coupled with the low transmission efficiency is the short flight distances recorded for whiteflies. This means that there is a higher likelihood of spread of CMGs within a field and to adjacent fields than to fields far from the infection focus. Detection of EACMV-associated symptoms at foci distant from the source of infection is therefore more likely to be spread via cutting infection than whitefly-borne mode of infection, unless the spread occurred via movement of wind-aided viruliferous whiteflies.
Plant parts liable to carry the pest in trade/transport | Pest stages | Borne internally | Borne externally | Visibility of pest or symptoms |
---|---|---|---|---|
Stems (above ground)/Shoots/Trunks/Branches | Yes | Pest or symptoms usually invisible |
Vector | Source | Reference | Group | Distribution |
---|---|---|---|---|
Bemisia tabaci | EFSA Panel on Plant Health (2013) | Insect |
The economic impact of EACMV-like viruses can only be deduced in the context of the documented impacts of cassava mosaic disease due to the commonness of mixed infections of CMGs under field conditions. Information is lacking on the impact of individual CMGs as this can only be achieved via controlled experiments with each virus under insect-proof screenhouses, which might be cost prohibitive.
The infamous regional CMD pandemic that occurred in the 1990s in East Africa was associated with a Ugandan variant of EACMV (EACMV-UG), a recombinant CMG parented by ACMV and EACMV (Gibson et al., 1996; Otim-Nape et al., 1997). The pandemic resulted in severe crop loss and famine-related deaths (Otim-Nape et al., 1998) reminiscent of the infamous potato late blight disease outbreak in Ireland in the nineteenth century (Alabi et al., 2015).
EACMV and other EACMV-like viruses can been diagnosed through various methods. The successful purification of CMGs (Bock et al., 1977) led to the development of various forms of enzyme-linked immunosorbent assay (ELISA) including double- (DAS) and triple- (TAS) antibody sandwich ELISAs capable of detecting the viruses in leaf extracts. Distinguishing between EACMV and other CMGs via ELISA could occur using a panel of discriminating monoclonal antibodies (Thomas et al., 1986; Harrison and Robinson, 1988; Ogbe et al., 1997). The different forms of ELISA are versatile and can be used to screen large field samples. However, ELISA is incapable of discriminating between the different EACMV-like viruses and their recombinant variants in mixed infections due to similarities in coat protein epitopes within CMGs (Thottapilly et al., 2003). Species specific oligonucleotide primers have been designed to target different genes encoded in the DNA A component of CMGs making it possible to differentiate between these viruses. During the early development of the PCR technique, viruses were detected in single-plex PCR but recently multiplex PCR assays capable of differentiating EACMV in mixed infections with other CMGs and cassava brown streak virus have been developed (Ndunguru et al., 2005; Ogbe et al., 2006; Alabi et al., 2008; Abarshi et al., 2012; Aloyce et al., 2013).
Symptoms caused by EACMV-like viruses are not distinguishable from those caused by other CMGs by visual inspection. However, mosaic patterns on cassava leaves indicate the presence of one or more of the CMD viruses, which can be discriminated using various diagnostic tools.
EACMV and other CMGs are indistinguishable from each other on the basis of foliar symptoms. Serological assays also have limitations in distinguishing CMGs. EACMV-type viruses can be distinguished from each other and from other CMGs using molecular diagnostics with virus-specific oligonucleotides.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Management of EACMV-associated CMD follows the same approach as other viral diseases on crops. Vector control through the use of insecticides is cost prohibitive and impracticable especially as cassava is considered as a minimal input crop in Africa. Two main approaches to CMD management are considered feasible, phytosanitation and breeding for resistance (Thresh and Otim-Nape, 1994). In theory, the two approaches applied singly or in combination should result in effective management of CMD caused by CMGs. However, there are bottle necks in their implementation. Phytosanitation was used effectively in Uganda to manage CMD over a period of time (Jameson, 1964). It involved releasing large quantities of virus-free plant materials to farmers to replace the rogued diseased plants accompanied by a heightened awareness campaign. Central to the success of this approach was the availability of a farmer-preferred cultivar multiplied on a large scale. However, this lapsed with the passage of time and the clean stock was lost in the process leading to the resurgence of CMGs and the associated pandemic.
The use of resistant/tolerant materials to control CMD coupled with phytosanitation and awareness is a more reliable control strategy. Many cassava varieties with demonstrable resistant traits have been used in various parts of Africa where cassava is grown. In Tanzania, studies on breeding for resistance started in the 1930s and 1940s and later spread to Madagascar and West Africa. In West Africa, the International Institute of Tropical Agriculture (IITA) pioneered the work and resistant lines from there were produced and shared with national breeding programmes across sub-Saharan Africa (Mahungu et al., 1994). But resistance breeding is a long term endeavor and sometimes promising resistant/tolerant lines may lack farmer-preferred traits due to linkage drag. Another major issue is effective deployment of resistant cultivars, when available. Consequently, CMD management becomes ineffective and slow. Besides, resistance could break down over time due to high disease and vector pressure, the emergence of resistance-breaking recombinant virus variants, etc. Recently, it has been shown that CMGs can produce virulence factors such as the so-called ‘Sequences enhancing geminivirus symptoms (SEGS)’ that help break down resistance in cassava.
In view of the benefits and limitations of each approach, a combination of both methods is encouraged in integrated pest management.
Alabi, O. J., 2009. Studies on epidemiology, molecular detection and genetic diversity of selected viruses infecting cassava and wine grapes. Washington, USA: Washington State University.
Bock KR, Woods RD, 1983. Etiology of African cassava mosaic disease. Plant Disease, 67(9):994-995
Brown, J. K., Fauquet, C. M., Briddon, R. W., Zerbini, F. M., Moriones, E., Navas-Castillo, J., 2012. Family Geminiviridae. In: Virus taxonomy. Ninth report of the international committee on taxonomy of viruses, [ed. by King, A. M. Q., Adams, M. J., Carstens, E. B., Lefkowitz, E. J.]. London, UK: Elsevier Academic Press. 351–373.
Chant SR, 1958. Studies on the transmission of cassava mosaic virus by Bemisia spp. (Aleyrodidae). Annals of Applied Biology, 46:210-215
Cossa, N. S., 2011. Epidemiology of cassava mosaic disease in Mozambique. Johannesburg, South Africa: University of Witwatersrand.
Cours G, 1951. Le manioc a Madagascar. Mémoires de l'Institut Scientifique de Madagascar. Série B Biologie Végétale, 3:203-400
EFSA Panel on Plant Health, 2013. Scientific Opinion on the risks to plant health posed by Bemisia tabaci species complex and viruses it transmits for the EU territory. EFSA Journal, 11(4). 3162. http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/3162.pdf
Jericho, C., Thompson, G. J., Gerntholtz, U., Viljoen, J. C., 1999. Occurrence and distribution of cassava diseases in South Africa. In: Proceedings of the Scientific Workshop of the Southern African Root Crops Research Network (SARRNET), Lusaka, Zambia, 17-19 August 1998 [ed. by Akoroda, M. O., Teri, J. M.]. 252- 262.
Johnson, A., 1992. Report, Lake Chad Farmer Training and Agricultural Development Project: American Organizations for Rehabilitation Through Training. Unpublished report. US Agency for International Development, Chad
Kamau, J., Sseruwagi, P., Aritua, V., 2005. Whiteflies as vectors of plant viruses in cassava and sweet potato in Africa: Kenya. In: Whiteflies and Whitefly-Borne Viruses in the Tropics: Building a Knowledge Base for Global Action, [ed. by Anderson, P. K., Morales, F.]. Cali, Colombia: Centro Internacional de Agricultura Tropical. 54–60.
Legg, J. P., 2010. Epidemiology of a whitefly-transmitted cassava mosaic geminivirus pandemic in Africa. In: Bemisia: Bionomics and Management of a Global Pest, [ed. by Stansly, P. A., Naranjo, S. E.]. Springer Science + Business Media B.V. 233-255.
Mabasa, K. G., 2007. Epidemiology of cassava mosaic disease and molecular characterization of cassava mosaic viruses and their associated whitefly Bemisia tabaci vector in South Africa. University of the Witwatersrand.
Ndunguru J, Legg JP, Aveling TAS, Thompson G, Fauquet CM, 2005. Molecular biodiversity of cassava begomoviruses in Tanzania:evolution of cassava geminiviruses in Africa and evidence for East Africa being a center of diversity of cassava geminiviruses. Virology Journal, 2, 21.
Ntonifor, N., James, B. D., Gbaguidi, B., Tumanteh, A., 2005. Whiteflies as vectors of plant viruses in cassava and sweetpotato in Africa: Cameroon. In: Whiteflies and Whitefly-Borne Viruses in the Tropics: Building a Knowledge Base for Global Action, [ed. by Anderson PK, Morales F]. Cali, Colombia: Centro Internacional de Agricultura Tropical. 40-45.
Ogbe FO, Legg J, Raya MD, Muimba-Kankalongo A, Theu MP, Kaitisha G, Phiri NA, Chalure A, 1997. Diagnostic survey of cassava mosaic viruses in Tanzania, Malawi and Zambia. Roots, 4:12-15
Stanley, J., Bisaro, D. M., Briddon, R. W. , Brown, J. K., Fauquet, C. M., Harrison, B. D., Rybicki, E. P., Stenger, D. C. , 2005. Family Geminiviridae. In: Virus Taxonomy: Eighth Report of the International Committee on Taxonomy of Viruses, [ed. by Fauquet, M. C., Mayo, M. A., Maniloff, J., Desselberger, U., Ball, L. A.]. London, UK: Elsevier Academic Press. 301–326.
Storey HH, Nichols RFW, 1938. Studies of the mosaic diseases of cassava. Annals of Applied Biology, 25:790-806
Thomas JE, Massalski PR, Harrison BD, 1986. Production of monoclonal antibodies to African cassava mosaic virus and differences in their reactivities with other whitefly-transmitted geminiviruses. Journal of General Virology, 67:2739-2748
Thresh, J. M., Hillocks, R. J., 2003. Cassava mosaic and cassava brown streak diseases in Nampula and Zambézia provinces of Mozambique. Roots , 8(2), 10–5.
Thresh, J. M., Mbwana, M. W., 1998. Cassava mosaic and cassava brown streak virus diseases in Zanzibar. Roots, 5(1), 6-9.
CABI, Undated. Compendium record. Wallingford, UK: CABI
Jericho C, Thompson GJ, Gerntholtz U, Viljoen JC, 1999. Occurrence and distribution of cassava diseases in South Africa. [Proceedings of the Scientific Workshop of the Southern African Root Crops Research Network (SARRNET), Lusaka, Zambia, 17-19 August 1998], [ed. by Akoroda MO, Teri JM]. 252-262.
Kamau J, Sseruwagi P, Aritua V, 2005. Whiteflies as vectors of plant viruses in cassava and sweet potato in Africa: Kenya. In: Whiteflies and Whitefly-Borne Viruses in the Tropics: Building a Knowledge Base for Global Action, [ed. by Anderson PK, Morales F]. Cali, Colombia: Centro Internacional de Agricultura Tropical. 54–60.
Ndunguru J, Legg JP, Aveling TAS, Thompson G, Fauquet CM, 2005. Molecular biodiversity of cassava begomoviruses in Tanzania:evolution of cassava geminiviruses in Africa and evidence for East Africa being a center of diversity of cassava geminiviruses. In: Virology Journal, 2 21.
Thresh JM, Hillocks RJ, 2003. Cassava mosaic and cassava brown streak diseases in Nampula and Zambézia provinces of Mozambique. In: Roots, 8 (2) 10–5.
09/10/17 Original text by:
Olufemi Joseph Alabi, Department of Plant Pathology & Microbiology, Texas A&M University AgriLife Research & Extension Center, Weslaco, USA
Rabson Mulenga, Zambia Agriculture Research Institute, Mount Makulu Central Research Station, Chilanga, Lusaka, Zambia
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