scholarly journals Spatial Analysis of Temporal Changes in the Pandemic of Severe Cassava Mosaic Disease in Northwestern Tanzania

2017 ◽  
Vol 107 (10) ◽  
pp. 1229-1242 ◽  
Author(s):  
A. M. Szyniszewska ◽  
C. Busungu ◽  
S. B. Boni ◽  
R. Shirima ◽  
H. Bouwmeester ◽  
...  
Keyword(s):  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
East African ◽  
Northwestern Tanzania ◽  
Direction Of Movement ◽  
Vector Borne ◽  
Sub Saharan ◽  
Associated Variables

To improve understanding of the dynamics of the cassava mosaic disease (CMD) pandemic front, geospatial approaches were applied to the analysis of 3 years’ data obtained from a 2-by-2° (approximately 222-by-222 km) area of northwestern Tanzania. In total, 80 farmers’ fields were assessed in each of 2009, 2010, and 2011, with 20 evenly distributed fields per 1-by-1° quadrant. CMD-associated variables (CMD incidence, CMD severity, vector-borne CMD infection, and vector abundance) increased in magnitude from 2009 to 2010 but showed little change from 2010 to 2011. Increases occurred primarily in the two westernmost quadrants of the study area. A pandemic “front” was defined by determining the values of CMD incidence and whitefly abundance where predicted disease gradients were greatest. The pandemic-associated virus (East African cassava mosaic virus-Uganda) and vector genotype (Bemisia tabaci sub-Saharan Africa 1–subgroup 1) were both present within the area bounded by the CMD incidence front but both also occurred ahead of the front. The average speed and direction of movement of the CMD incidence front (22.9 km/year; southeast) and whitefly abundance front (46.6 km/year; southeast) were calculated, and production losses due to CMD were estimated to range from US$4.3 million to 12.2 million.

scholarly journals First Report of East African Cassava Mosaic Begomovirus in Nigeria

Plant Disease ◽  
1999 ◽  
Vol 83 (4) ◽  
pp. 398-398 ◽  
Author(s):  
F. O. Ogbe ◽  
G. I. Atiri ◽  
D. Robinson ◽  
S. Winter ◽  
A. G. O. Dixon ◽  
...  
Keyword(s):  
Central Africa ◽  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
Cassava Mosaic Disease ◽  
Enzyme Linked Immunosorbent Assay ◽  
East African ◽  
African Countries ◽  
Manihot Esculenta Crantz ◽  
Cross River State ◽  
Sub Saharan

Cassava (Manihot esculenta Crantz) is an important food crop in sub-Saharan Africa. One of the major production constraints is cassava mosaic disease caused by African cassava mosaic (ACMV) and East African cassava mosaic (EACMV) begomoviruses. ACMV is widespread in its distribution, occurring throughout West and Central Africa and in some eastern and southern African countries. In contrast, EACMV has been reported to occur mainly in more easterly areas, particularly in coastal Kenya and Tanzania, Malawi, and Madagascar. In 1997, a survey was conducted in Nigeria to determine the distribution of ACMV and its strains. Samples from 225 cassava plants showing mosaic symptoms were tested with ACMV monoclonal antibodies (MAbs) in triple antibody sandwich enzyme-linked immunosorbent assay (1). Three samples reacted strongly with MAbs that could detect both ACMV and EACMV. One of them did not react with ACMV-specific MAbs while the other two reacted weakly with such MAbs. With polymerase chain reaction (2), the presence of EACMV and a mixture of EACMV and ACMV in the respective samples was confirmed. These samples were collected from two villages: Ogbena in Kwara State and Akamkpa in Cross River State. Co-infection of some cassava varieties with ACMV and EACMV leads to severe symptoms. More importantly, a strain of mosaic geminivirus known as Uganda variant arose from recombination between the two viruses (2). This report provides evidence for the presence of EACMV in West Africa. References: (1) J. E. Thomas et al. J. Gen. Virol. 67:2739, 1986. (2) X. Zhou et al. J. Gen. Virol. 78:2101, 1997.

scholarly journals Genetic diversity and phylogeography of cassava mosaic viruses in Kenya

2006 ◽  
Vol 87 (10) ◽  
pp. 3053-3065 ◽  
Author(s):  
Simon E. Bull ◽  
Rob W. Briddon ◽  
William S. Sserubombwe ◽  
Kahiu Ngugi ◽  
Peter G. Markham ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Central Africa ◽  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Polymorphism Analysis ◽  
Virus Species ◽  
East African ◽  
Virus Diversity

Cassava is a major factor in food security across sub-Saharan Africa. However, the crop is susceptible to losses due to biotic stresses, in particular to viruses of the genus Begomovirus (family Geminiviridae) that cause cassava mosaic disease (CMD). During the 1990s, an epidemic of CMD severely hindered cassava production across eastern and central Africa. A significant influence on the appearance of virus epidemics is virus diversity. Here, a survey of the genetic diversity of CMD-associated begomoviruses across the major cassava-growing areas of Kenya is described. Because an initial PCR-restriction fragment-length polymorphism analysis identified a much greater diversity of viruses than assumed previously, representative members of the population were characterized by sequence analysis. The full-length sequences of 109 components (68 DNA-A and 41 DNA-B) were determined, representing isolates of East African cassava mosaic virus and East African cassava mosaic Zanzibar virus, as well as a novel begomovirus species for which the name East African cassava mosaic Kenya virus is proposed. The DNA-B components were much less diverse than their corresponding DNA-A components, but nonetheless segregated into western and eastern (coastal) groups. All virus species and strains encountered showed distinct geographical distributions, highlighting the importance of preventing both the movement of viruses between these regions and the importation of the disease from adjacent countries and islands in the Indian Ocean that would undoubtedly encourage further diversification.

scholarly journals Variants of East African cassava mosaic virus and Its Distribution in Double Infections with African cassava mosaic virus in Nigeria

Plant Disease ◽  
2003 ◽  
Vol 87 (3) ◽  
pp. 229-232 ◽  
Author(s):  
F. O. Ogbe ◽  
G. Thottappilly ◽  
A. G. O. Dixon ◽  
G. I. Atiri ◽  
H. D. Mignouna
Keyword(s):  
Mosaic Virus ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Single Infection ◽  
East African ◽  
Humid Forest ◽  
Forest Region ◽  
Agroecological Zones ◽  
Cassava Mosaic Virus

In a survey for cassava mosaic begomoviruses conducted in 1997 and 1998 in Nigeria, East African cassava mosaic virus (EACMV) was detected by the polymerase chain reaction together with African cassava mosaic virus (ACMV) in 27 out of 290 cassava leaf samples of infected plants from 254 farmers' fields in five agroecological zones. One plant was infected with EACMV only. Five variant isolates of EACMV were observed based on their reactions to primers that could detect Cameroonian and East African strains of EACMV. Isolates of variants 1 and 3 occurred mostly in the derived or coastal and southern Guinea savannahs, while variants 4 and 5 predominated in the humid forest region. Isolates of variant 2 were widely distributed across the three agroecologies. EACMV was not detected in the northern Guinea savannah and arid and semiarid zones. Most doubly infected plants showed more severe symptoms than plants with single infection. Occurrence of EACMV variants together with ACMV detection and information about their distribution in Nigeria could be used for the selection of cassava clones in cassava mosaic disease resistance programs.

scholarly journals Recombination, pseudorecombination and synergism of geminiviruses are determinant keys to the epidemic of severe cassava mosaic disease in Uganda

2001 ◽  
Vol 82 (3) ◽  
pp. 655-665 ◽  
Author(s):  
J. S. Pita ◽  
V. N. Fondong ◽  
A. Sangaré ◽  
G. W. Otim-Nape ◽  
S. Ogwal ◽  
...  
Keyword(s):  
Mosaic Virus ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
East African ◽  
Recombinant Fragment ◽  
Complete Sequences ◽  
Natural Recombination ◽  
Cassava Mosaic Virus

The molecular variability of cassava geminiviruses occurring in Uganda was investigated in this study. Infected cassava plants and whiteflies were collected from cassava plantings in different geographical areas of the country and PCR was used for molecular characterization of the viruses. Two complete sequences of DNA-A and -B from African cassava mosaic virus (ACMV), two DNA-A sequences from East African cassava mosaic virus (EACMV), two DNA-B sequences of EACMV and the partial DNA-A nucleotide sequence of a new virus strain isolated in Uganda, EACMV-UG3, are reported here. Analysis of naturally infected cassava plants showed various assortments of DNA-A and DNA-B of the Ugandan viruses, suggesting the occurrence of natural inter- and intraspecies pseudorecombinations and a pattern of cassava mosaic disease (CMD) more complex than previously reported. EACMV-UG2 DNA-A, which contains a recombinant fragment between ACMV and EACMV-UG1 in the coat protein gene that resembles virus from Tanzania, was widespread in the country and always associated with EACMV-UG3 DNA-B, which probably resulted from another natural recombination event. Mixed infections of ACMV-UG and EACMV-UG in cassava and whiteflies were detected in most of the regions where both viruses occurred. These mixed-infected samples always showed extremely severe CMD symptoms, suggesting a synergistic interaction between ACMV-UG and EACMV-UG2. The first demonstration is provided of infectivity of EACMV clones to cassava, proving conclusively that the pseudorecombinant EACMV-UG2 DNA-A+EACMV-UG3 DNA-B is a causal agent of CMD in Uganda.

scholarly journals Genetic Diversity of Mitochondrial DNA of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Associated with Cassava and the Occurrence of Cassava Mosaic Disease in Zambia

Insects ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 761
Author(s):  
Patrick Chiza Chikoti ◽  
Mathias Tembo ◽  
James Peter Legg ◽  
Rudolph Rufini Shirima ◽  
Habibu Mugerwa ◽  
...  
Keyword(s):  
Bemisia Tabaci ◽  
Control Strategies ◽  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
Cassava Mosaic Disease ◽  
Northern Province ◽  
Western Province ◽  
Key Factor ◽  
Sub Saharan ◽  
Brown Streak

Bemisia tabaci is an important vector of cassava brown streak viruses and cassava mosaic begomoviruses, the causal agents of cassava brown streak disease and cassava mosaic disease (CMD), respectively. A study was carried out to determine the genetic variability of B. tabaci associated with cassava and the occurrence of CMD in Zambia in 2013 and 2015. Phylogenetic analysis showed the presence of only the sub-Saharan Africa 1 (SSA1) genetic group in Zambia. The SSA1 population had three population subgroups (SGs): SSA1-SG1, SSA1-SG2 and SSA1-SG3. All three SSA1 population subgroups occurred in Western Province. However, only SSA1-SG3 occurred in Eastern Province, while only SSA1-SG1 occurred in North Western and Luapula Provinces. Adult B. tabaci were most abundant in Western Province in 2013 (11.1/plant) and 2015 (10.8/plant), and least abundant (0.2/plant) in Northern Province in both 2013 and 2015. CMD was prevalent in all seven provinces surveyed, with the highest incidence recorded in Lusaka Province in both 2013 (78%) and 2015 (83.6%), and the lowest in Northern Province in both 2013 (26.6%) and 2015 (29.3%). Although SSA1-SG1 occurred at greater abundances than the other subgroups, there was no direct association demonstrated between whitefly subgroup and incidence of CMD. Establishing which B. tabaci genetic groups and populations are associated with CMD and their distribution in the country is a key factor in guiding the development of CMD control strategies for cassava-dependent households.

scholarly journals Validation of high rates of nucleotide substitution in geminiviruses: phylogenetic evidence from East African cassava mosaic viruses

2009 ◽  
Vol 90 (6) ◽  
pp. 1539-1547 ◽  
Author(s):  
Siobain Duffy ◽  
Edward C. Holmes
Keyword(s):  
Nucleotide Substitution ◽  
Central Africa ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
East African ◽  
Substitution Rates ◽  
Leaf Curl Virus ◽  
Intensive Sampling ◽  
Major Pathogens

Whitefly-transmitted geminiviruses are major pathogens of the important crop cassava in Africa. The intensive sampling and sequencing of cassava mosaic disease-causing viruses that occurred in the wake of a severe outbreak in Central Africa (1997–2002) allowed us to estimate the rate of evolution of this virus. East African cassava mosaic virus and related species are obligately bipartite (DNA-A and DNA-B segments), and these two genome segments have different evolutionary histories. Despite these phylogenetic differences, we inferred high rates of nucleotide substitution in both segments: mean rates of 1.60×10−3 and 1.33×10−4 substitutions site−1 year−1 for DNA-A and DNA-B, respectively. While similarly high substitution rates were found in datasets free of detectable recombination, only that estimated for the coat protein gene (AV1), for which an additional DNA-A sequence isolated in 1995 was available, was statistically robust. These high substitution rates also confirm that those previously estimated for the monopartite tomato yellow leaf curl virus (TYLCV) are representative of multiple begomoviruses. We also validated our rate estimates by comparing them with those depicting the emergence of TYLCV in North America. These results further support the notion that geminiviruses evolve as rapidly as many RNA viruses.

scholarly journals Survey, Molecular Detection, and Characterization of Geminiviruses Associated with Cassava Mosaic Disease in Zambia

Plant Disease ◽  
2016 ◽  
Vol 100 (7) ◽  
pp. 1379-1387 ◽  
Author(s):  
Rabson M. Mulenga ◽  
James P. Legg ◽  
Joseph Ndunguru ◽  
Douglas W. Miano ◽  
Eunice W. Mutitu ◽  
...  
Keyword(s):  
Mosaic Virus ◽  
Mosaic Disease ◽  
Disease Spread ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Virus Infections ◽  
East African ◽  
A Genome ◽  
The Status ◽  
Cassava Mosaic Virus

A survey was conducted from April to May 2014 in 214 farmers’ fields located across six major cassava-producing provinces (Western, Northwestern, Northern, Luapula, Lusaka, and Eastern) of Zambia to determine the status of cassava mosaic disease (CMD) and the species diversity of associated cassava mosaic geminiviruses (CMG). Mean CMD incidence varied across all six provinces but was greatest in Lusaka Province (81%) and least in Northern Province (44%). Mean CMD severity varied slightly between provinces, ranging from 2.78 in Eastern Province to 3.00 in Northwestern Province. Polymerase chain reaction discrimination of 226 survey samples, coupled with complete DNA-A genome sequence analysis, revealed the presence of African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and East African cassava mosaic Malawi virus (EACMMV) as single or mixed infections of different proportions. Single-virus infections were predominant, occurring in 62.8% (ACMV), 5.8% (EACMMV), and 2.2% (EACMV) of samples relative to mixed-virus infections, which occurred in 19.5% (ACMV + EACMMV), 0.4% (ACMV + EACMV), and 0.9% (ACMV + EACMV + EACMMV) of samples. Phylogenetic analysis revealed the segregation of virus isolates from Zambia into clades specific to ACMV, EACMV, and EACMMV, further confirming the presence of all three viruses in Zambia. The results point to a greater diversity of CMG across major cassava-growing provinces of Zambia and implicate contaminated cassava cuttings in disease spread.

scholarly journals Two Novel DNAs That Enhance Symptoms and Overcome CMD2 Resistance to Cassava Mosaic Disease

2016 ◽  
Vol 90 (8) ◽  
pp. 4160-4173 ◽  
Author(s):  
Joseph Ndunguru ◽  
Leandro De León ◽  
Catherine D. Doyle ◽  
Peter Sseruwagi ◽  
German Plata ◽  
...  
Keyword(s):  
Mosaic Virus ◽  
Dna Sequences ◽  
Large Scale ◽  
Indian Subcontinent ◽  
Mosaic Disease ◽  
African Cassava Mosaic Virus ◽  
Cassava Mosaic Disease ◽  
Resistance Locus ◽  
East African ◽  
Cassava Mosaic Virus

ABSTRACTCassava mosaic begomoviruses (CMBs) cause cassava mosaic disease (CMD) across Africa and the Indian subcontinent. Like all members of the geminivirus family, CMBs have small, circular single-stranded DNA genomes. We report here the discovery of two novel DNA sequences, designated SEGS-1 and SEGS-2 (forsequencesenhancinggeminivirussymptoms), that enhance symptoms and break resistance to CMD. The SEGS are characterized by GC-rich regions and the absence of long open reading frames. Both SEGS enhanced CMD symptoms in cassava (Manihot esculentaCrantz) when coinoculated withAfrican cassava mosaic virus(ACMV),East African cassava mosaic Cameroon virus(EACMCV), orEast African cassava mosaic virus-Uganda(EACMV-UG). SEGS-1 also overcame resistance of a cassava landrace carrying the CMD2 resistance locus when coinoculated with EACMV-UG. Episomal forms of both SEGS were detected in CMB-infected cassava but not in healthy cassava. SEGS-2 episomes were also found in virions and whiteflies. SEGS-1 has no homology to geminiviruses or their associated satellites, but the cassava genome contains a sequence that is 99% identical to full-length SEGS-1. The cassava genome also includes three sequences with 84 to 89% identity to SEGS-2 that together encompass all of SEGS-2 except for a 52-bp region, which includes the episomal junction and a 26-bp sequence related to alphasatellite replication origins. These results suggest that SEGS-1 is derived from the cassava genome and facilitates CMB infection as an integrated copy and/or an episome, while SEGS-2 was originally from the cassava genome but now is encapsidated into virions and transmitted as an episome by whiteflies.IMPORTANCECassava is a major crop in the developing world, with its production in Africa being second only to maize. CMD is one of the most important diseases of cassava and a serious constraint to production across Africa. CMD2 is a major CMD resistance locus that has been deployed in many cassava cultivars through large-scale breeding programs. In recent years, severe, atypical CMD symptoms have been observed occasionally on resistant cultivars, some of which carry the CMD2 locus, in African fields. In this report, we identified and characterized two DNA sequences, SEGS-1 and SEGS-2, which produce similar symptoms when coinoculated with cassava mosaic begomoviruses onto a susceptible cultivar or a CMD2-resistant landrace. The ability of SEGS-1 to overcome CMD2 resistance and the transmission of SEGS-2 by whiteflies has major implications for the long-term durability of CMD2 resistance and underscore the need for alternative sources of resistance in cassava.

scholarly journals Detecting cassava mosaic disease using a deep residual convolutional neural network with distinct block processing

2021 ◽  
Vol 7 ◽  
pp. e352
Author(s):  
David Opeoluwa Oyewola ◽  
Emmanuel Gbenga Dada ◽  
Sanjay Misra ◽  
Robertas Damaševičius
Keyword(s):  
Neural Network ◽  
Convolutional Neural Network ◽  
Mosaic Disease ◽  
Sub Saharan Africa ◽  
Cassava Mosaic Disease ◽  
Low Contrast ◽  
Block Processing ◽  
Color Separation ◽  
Distinct Block ◽  
Sub Saharan

For people in developing countries, cassava is a major source of calories and carbohydrates. However, Cassava Mosaic Disease (CMD) has become a major cause of concern among farmers in sub-Saharan Africa countries, which rely on cassava for both business and local consumption. The article proposes a novel deep residual convolution neural network (DRNN) for CMD detection in cassava leaf images. With the aid of distinct block processing, we can counterbalance the imbalanced image dataset of the cassava diseases and increase the number of images available for training and testing. Moreover, we adjust low contrast using Gamma correction and decorrelation stretching to enhance the color separation of an image with significant band-to-band correlation. Experimental results demonstrate that using a balanced dataset of images increases the accuracy of classification. The proposed DRNN model outperforms the plain convolutional neural network (PCNN) by a significant margin of 9.25% on the Cassava Disease Dataset from Kaggle.

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