Publications (27)25.29 Total impact
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Article: Response of Local Cassava Varieties in Uganda to Cassava Mosaic Virus Disease
American Journal of Experimental Agriculture. 01/2012; 2(1):111-132. -
Article: Response of improved cassava varieties in Uganda to cassava mosaic disease (CMD) and their inherent resistance mechanisms
African journal of agricultural research 01/2011; 6(3):521-531. · 0.08 Impact Factor -
Article: Temporal spread of cassava mosaic virus disease in a range of cassava cultivars in different agro‐ecological regions of Uganda
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ABSTRACT: The spread of cassava mosaic disease (CMD) in a range of cassava cultivars was studied in experiments and on-farm trials in different agro-ecological regions of Uganda in 1989–1990 and 1990–1991. No spread occurred in either experiment at the southernmost site near Kampala, but there was considerable spread at the four sites elsewhere and also in the on-farm trials in Luwero district. There were significant differences in the final incidence of disease between locations and between cultivars at each location. Where spread occurred it was more rapid in the Ugandan cvs Ebwanateraka, Senyonjo and Bao than in four of the five improved TMS cultivars introduced from Nigeria. These usually showed an apparent decline in incidence of CMD after reaching maxima 4 to 8 months after planting (MAP). The areas under the disease progress curves (AUDPCs) differed significantly between locations and cultivars and were less for cvs TMS 30572, TMS 30395, TMS 30337 and TMS 60142 than for cvs Ebwanateraka, Senyonjo, Bao and TMS 30786. Overall, the mean AUDPCs were greatest at Migyera in Luwero district in 1989–1990 and at Kagando in Kasese district in 1990–1991. They were significantly less at Mubuku in Kasese district in 1989–1990 than at the other two experimental sites where spread occurred. Adult whitefly vector populations were highest at Migyera and Kagando in the 1989–1990 and 1990–1991 trials, respectively, and they were higher on cvs Bao, Ebwanateraka and TMS 30786 than on other varieties. Mean numbers of adults increased until 3–5 MAP and then declined, but CMD incidence increased progressively to reach maxima at or near crop maturity. Locations with the largest numbers of adults also had a relatively high incidence of CMD. Symptoms of CMD were usually more severe on cvs Ebwanateraka, Bao and Bukalasa 11 than on the TMS cultivars, on which symptoms remained slight throughout growth and usually decreased from 5 MAP. The differences between sites, the resistance of the cultivars and the relationship between CMD incidence and whitefly populations are discussed.Annals of Applied Biology 06/2008; 133(3):415 - 430. · 2.18 Impact Factor -
Article: The effects of cassava mosaic virus disease on yield and compensation in mixed stands of healthy and infected cassava
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ABSTRACT: The effects of cassava mosaic virus disease (CMD) on yield in fully and partly infected stands of cassava were investigated in field trials in Uganda in 1990-91 and 1991-92. Three cultivars (Ebwanateraka, Bao and Bukalasa 1 l), each at three levels of cutting infection (O%, 50% and 100%) and harvested 510 and 15 months after planting (MAP) were used in a randomised block design with split-split plots and four replicates. Moreover, yield and growth data for individual infected and uninfected plants were considered in relation to the health status of their nearest neighbours. In each experiment, fresh tuberous root yields of plants from 100% infected plots gave sigdicantly lower yields than those from 0% or 50% infected plots at each harvest date and the losses were greatest in cv. Bao. Yields of plants from 0% and 50% plots for each of the three cultivars were not significantly different, 10 and 15 MAP. The loss in yield differed between cultivars and harvest dates. Fresh stem, leaf and root yields and the number of tuberous roots were influenced by the health status of the plants harvested and that of their nearest neighbours. Uninfected plants surrounded by infected ones had more roots and heavier total fresh root, stem and leaf weights than those surrounded by uninfected ones. Overall, 26% and 42% compensation was recorded in 1990-91 and 1991-92, respectively. The effects of CMD on cassava production and of compensation in mixed stands of infected and uninfected plants are discussed, especially in relation to control strategies such as roguing.Annals of Applied Biology 06/2008; 130(3):503 - 521. · 2.18 Impact Factor -
Article: The Spread of African Cassava Mosaic Virus into and within Cassava Fields
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ABSTRACT: Only a small proportion of Bemisia tabaci collected in totally infected cassava fields at a site in Côte d'lvoire transmitted African cassava mosaic virus (ACMV) to test plants. Nevertheless, the monthly increase in disease incidence in an experimental planting was directly related to numbers of adult whiteflies counted on plants 6 weeks earlier.In plots at different spacings, the greatest incidence of ACMV expressed as a percentage of the total stand occurred at the lowest plant density. Much speread into the spacing trial and into two other experimental plantings occurred from outside sources and followed downwind gradients. By contrast, spread from ACMV-infected sources within plantings was limited. It occurred in all directions but over distances of only a few metres. These contrasting patterns of spread are attributed to the differentbehavior of B. tabaci above and within the crop canopy.It is concluded that contamination of cassava fields in the coastal forest area of Côte d'Ivoire is due mainly to rapid spread from outside sources which leads to internal foci that contribute to some further, although limited, spread. These findings are discussed in relation to possible control strategies based on the release of healthy cuttings, dense planting and subsequent roguing. Such measures are unlikely to be effectve in the coastal forest region of Côte d'Ivoire and adjacent countriesunless varieties are grown with greater resistance to infection than those currently used.Journal of Phytopathology 06/2008; 130(4):289 - 302. · 0.79 Impact Factor -
Article: Progress of cassava mosaic virus disease and whitefly vector populations in single and mixed stands of four cassava varieties grown under epidemic conditions in Uganda
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ABSTRACT: Progress curves of cassava mosaic virus disease (CMD) and populations of the whitefly vector (Bemisia tabaci) were assessed using four cassava varieties grown alone and as a random mixture in two experiments established under epidemic conditions at a site near Kampala in southern Uganda. There were significant differences in final CMD incidence and in the areas under the disease progress curves between varieties when grown alone and as a mixture in both experiments. Variety Ebwanateraka had the highest incidence and SS4 the lowest, even though it supported the largest populations of adult whiteflies. The overall incidence of CMD in the mixture was similar to that in pure stands of the partially resistant Nase 2 and greater than in the resistant Migyera and SS4. Compared to pure stands, incidence of CMD in each component of the mixture was reduced significantly only in Ebwanateraka, whereas vector populations were less only in SS4 and Nase 2. On several observation dates the actual incidence of CMD and populations of adult whiteflies in the mixture were significantly less than expected values estimated from the results for the four varieties when each was grown alone. A highly significant positive relationship was established for each variety between peak populations of adult whitefly and leaf area index at the time. The implications of the findings and the scope for future research on the use of varietal mixtures for the management of CMD are discussed.Annals of Applied Biology 06/2006; 138(2):161 - 170. · 2.18 Impact Factor -
Article: Molecular ecology and emergence of tropical plant viruses.
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ABSTRACT: An appreciation of the risks caused by emergent plant viruses is critical in tropical areas that rely heavily on agriculture for subsistence and rural livelihood. Molecular ecology, within 10 years, has unraveled the factors responsible for the emergence of several of the economically most important tropical plant viruses: Rice yellow mottle virus (RYMV), Cassava mosaic geminiviruses (CMGs), Maize streak virus (MSV), and Banana streak virus (BSV). A large range of mechanisms--most unsuspected until recently--were involved: recombination and synergism between virus species, new vector biotypes, genome integration of the virus, host adaptation, and long-distance dispersal. A complex chain of molecular and ecological events resulted in novel virus-vector-plant-environment interactions that led to virus emergence. It invariably involved a major agricultural change: crop introduction, cultural intensification, germplasm movement, and new genotypes. A current challenge is now to complement the analysis of the causes by an assessment of the risks of emergence. Recent attempts to assess the risks of emergence of virulent virus strains are described.Annual Review of Phytopathology 02/2006; 44:235-60. · 9.88 Impact Factor -
Chapter: Virus Resistance in Rice
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ABSTRACT: The genus Oryza of the Family Gramineae comprises 18 tropical and subtropical species, of which two species are cultivated as rice: O. sativa and O. glaberrima. Rice provides the staple food of 60% of mankind, and is cultivated in all tropical and subtropical countries. Oryza sativa is thought to have been domesticated in China before 6500 BC, in India between 2000 and 1500 BC and even earlier than 5000 BC in northeast India (Chauvet, 2004). Molecular markers strongly suggested that the asian rice has been domesticated twice independently to give rise to the so-called japonica and indica groups of varieties similar to subspecies in China and South-India, respectively (Second, 1982). A third domestication took place in West Africa probably around 1500 BC from the wild relative O. brevigulata (syn. O. barthii) to give the african cultivated rice species O. glaberrima which is isolated from O. sativa by reproductive barriers (Oka, 1958; Second, 1982). Rice is a natural host for 20 viruses and an experimental host for 17. About 16 viruses may seriously affect rice yield (Lapierre and Signoret, 2004). The distribution of each virus is generally restricted to only one of the continents in which rice is grown. Host plant resistance has been reported for several viruses. Intensive breeding programs have been carried out to obtain resistance to the main virus diseases: rice tungro viruses and Rice stripe virus in Asia, Rice hoja blanca virus in South-America, and Rice yellow mottle virus in Africa.12/2005: pages 431-446; -
Article: Dual begomovirus infections and high Bemisia tabaci populations: two factors driving the spread of a cassava mosaic disease pandemic
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ABSTRACT: A cassava mosaic disease (CMD) pandemic currently affects much of East and Central Africa. To understand the factors driving the pandemic's continued spread, complementary data sets were collected from cassava plots, planted with healthy cuttings, at eight sites along a north–south transect in southern Uganda, through the pandemic's leading edge. Data were collected on virus incidence, symptom severity, populations of the whitefly vector, Bemisia tabaci, their infectivity and ability to transmit different viruses. In 1996, 6 months after planting, CMD incidences were highest at sites 1 and 2, then decreased progressively until site 6, and remained low at sites 7 and 8. The largest B. tabaci populations also occurred at northernmost sites, 1–3. In 1997, CMD incidence increased significantly at sites 5–8 and this was associated with significant increases in the B. tabaci populations. The pandemic's spread was also associated with significant increases in the percentage of dual infections of East African cassava mosaic virus-Uganda and African cassava mosaic virus, which caused the severest symptoms and the greatest reduction in leaf area. Whitefly adults collected from within the pandemic area were infective, whereas those collected ahead of the pandemic were not. The transmission rate of African cassava mosaic virus from plants with dual infections was significantly less than that of East African cassava mosaic virus-Uganda, which may explain the latter's predominance within the pandemic. These results show that the arrival of East African cassava mosaic virus-Uganda into areas affected previously only by African cassava mosaic virus, has resulted in novel virus/vector/host–plant interactions that drive the pandemic's continued spread.Plant Pathology 09/2004; 53(5):577 - 584. · 2.13 Impact Factor -
Article: Methods of surveying the incidence and severity of cassava mosaic disease and whitefly vector populations on cassava in Africa: a review.
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ABSTRACT: Field surveys in many cassava growing areas of Africa have assessed the incidence and severity of cassava mosaic disease (CMD), populations of the whitefly vector (Bemisia tabaci), and the distribution of cassava mosaic begomoviruses (CMBs). The methods employed differ greatly between countries and attempts at standardization were made in recent CMD surveys in East and Central Africa, notably in the systemwide Whitefly IPM Project, which provides a paradigm for future work on CMBs and whiteflies on cassava in Africa and also elsewhere. However, there is a need for greater standardization so as to assess the continued expansion of the current CMD pandemic in eastern Africa. Standardized methods will facilitate the collection of reliable data, which can be used to predict future disease spread, develop appropriate management strategies and compare disease development between seasons and locations. In this review, the methods used and the problems encountered during such surveys are discussed and recommendations made on future procedure.Virus Research 04/2004; 100(1):129-42. · 2.94 Impact Factor -
Article: Cassava mosaic virus disease in East Africa: a dynamic disease in a changing environment.
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ABSTRACT: Cassava mosaic disease (CMD), now known to be caused by cassava mosaic geminiviruses (Family Geminiviridae; Genus Begomovirus), was first reported in East Africa in 1894. Epidemics occurred in Madagascar and Uganda in the 1930s and 1940s, and more localised rapid spread of CMD was observed in parts of coastal Tanzania in the 1930s and coastal Kenya in the 1970s. During the 1990s, a major regional pandemic of an unusually severe form of CMD has expanded to affect parts of at least five countries, causing massive economic losses and destabilising food security. Mechanisms responsible for the development and progress of the pandemic have been described, and comparisons of epidemiological data for varieties grown throughout the period under review suggest that the recent pandemic has been characterised by rapid rates of CMD spread hitherto unknown in East Africa. A key factor in the genesis and spread of the pandemic has been the recombination between two distinct cassava mosaic geminiviruses to produce a novel and more virulent hybrid. Although such events may be common, the known history of CMD in East Africa suggests that the frequency with which they become epidemiologically significant is low. A corollary of this is that resistance, developed originally in Tanzania between 1934 and 1960, and utilized and supplemented at the International Institute of Tropical Agriculture, Nigeria, since 1971, is providing effective CMD control in current pandemic-affected areas of East Africa. Consequently, it is concluded that prospects for managing CMD in the 21st century are good, and that the approach adopted should build on the model of collaborative research and implementation that has been established in tackling the current CMD pandemic.Virus Research 12/2000; 71(1-2):135-49. · 2.94 Impact Factor -
Article: The Components and Deployment of Resistance to Cassava Mosaic Virus Disease
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ABSTRACT: Cassava mosaic virus disease (CMD) is prevalent and causes serious losses in cassava (Manihot esculenta) in southern India and in many parts of sub-Saharan Africa. The disease is caused by viruses of the Geminiviridae that are transmitted by the whitefly Bemisia tabaci and disseminated in the stem cuttings used routinely for propagation. The main approach to control is through the use of virus-resistant varieties, but suitable ones are not always available and susceptible varieties are still widely grown. This explains why CMD continues to be a problem in many areas.CMD-resistant varieties have several features which are considered in this review:- They are not readily infected, even when exposed to large amounts of vector-borne inoculum. When infected they develop symptoms that tend to be inconspicuous and not associated with obvious deleterious effects on growth or yield. Moreover, the symptoms become even less conspicuous as growth proceeds and plants may eventually recover and become symptomless. Infected plants support a low virus content and they are likely to be a poor source of inoculum from which further spread can occur. Virus is not fully systemic within infected plants which can be a source of uninfected planting material when stem cuttings are collected for further propagation. This phenomenon is referred to as reversion and it has an important cleansing effect in restricting or preventing the progressive deterioration in health status that would otherwise occur during successive cycles of vegetative propagation.The available information on the different components of resistance is discussed and it is concluded that they are inter-related features of the same basic mechanism that restricts virus entry, replication and movement within the host. It is argued that the effectiveness and durability of virus-resistant varieties are likely to be influenced by the way in which they are deployed. However, this topic has received little attention from researchers and there is continuing uncertainty on the effects of CMD on the yield of resistant varieties and on the role of phytosanitation. This involves the use of virus-free planting material and the removal (roguing) of any additional diseased plants that occur. Some consider that these procedures complement the use of virus-resistant varieties and should be adopted, whereas others argue that they are unnecessary and inappropriate. It is concluded that there is considerable scope for utilizing resistant varieties more widely and more effectively than at present, but in doing so it is important to avoid eroding the genetic diversity that is currently such a marked feature of cassava cultivation in Africa.Integrated Pest Management Reviews 11/1998; 3(4):209-224. -
Article: The effects of African cassava mosaic geminivirus on the growth and yield of cassava in Uganda
Tropical Science. 01/1994; 34(1):43-54. -
Article: Control of Plant Virus Diseases in Sub-Saharan Africa: the Possibility and Feasibility of an Integrated Approach
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ABSTRACT: Plant viruses and virus diseases have been studied for more than 100 years and much attention has been given to their control. However, this has been difficult to achieve because of the lack of any effective means of curing virus-infected plants. Chemotherapy, thermotherapy and meristem-tip culture can be successful, but they cannot be used on a large scale. Consequently, the main approach has been to prevent or delay virus infection or to ameliorate its effects. Various means have been used to achieve these objectives, including phytosanitation (involving quarantine measures, crop hygiene, use of virus-free planting material and eradication), changes in cropping practices, use of pesticides to control vectors, mild strain protection and the deployment of resistant or tolerant varieties. These measures can be used singly or in combination so as to exploit synergistic interactions. This paper considers the advantages of an integrated approach and provides selected examples from experience with several important African diseases, including cocoa swollen shoot, cassava mosaic and groundnut rosette. It is emphasised that much detailed research and a thorough knowledge of farming practices is required before an effective integrated programme can be developed and promoted. There are also formidable problems in ensuring adoption because of the generally limited education and resources of farmers in most parts of sub-Saharan Africa and the severe constraints imposed by the cropping practices adopted. Nevertheless, integrated control measures have evident benefits and should be fostered and promoted as a means of enhancing crop productivity to meet the increasing demands of a burgeoning human population.African Crop Science Journal (ISSN: 1021-9730) Vol 11 Num 3. -
Article: Analysis and Modelling of the Temporal Spread of African Cassava Mosaic Virus and Implications for Disease Control
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ABSTRACT: This paper reports the main conclusions of a series of experiments concluded at Adiopodoume in the forest zone of the Ivory Coast between 1980 and 1990 on the temporal spread of African cassava mosaic virus (ACMV). The experiments sought to gain a better understanding of the epidemiology of the disease it causes and to facilitate the assessment of control measure. The course of ACMV epidemics over time was shown to depend closely on crop age and planting date. These relationships were expressed mathematically and ACMV progress curves were modeled combining a direct interaction between an overall exponential decreasing susceptibility to infection with crop age and a sinusoidal temperature-driven seasonal fluctuation in amount of spread from outside sources. After being validated using 1930s data from Kiwanda in Tanzania, this model was extended to incorporate host plant resistance, spread within plantings and yield losses. Simulation studies showed that when reversion (non-systemicity of the virus) does not occur and when cuttings are not selected preferentially from healthy plants, disease incidence increased in successive plantings of the same clonal stock and ultimately reached 100%. This occurred whatever the degree of host resistance, albeit after different periods. By contrast, with reversion and/or cutting selection, disease incidence may reach equilibrium values below 100% in resistant cultivars. At such equilibria, the effects of reversion and/or cutting selection balance the new virus transmissions by whiteflies. This emphasizes the potential of resistant cultivars to control ACMV by exploiting their ability to revert, as such cultivars not only suffer yield loss when infected, but are less likely to become heavily infected, even after many cycles of crop production.African Crop Science Journal (ISSN: 1021-9730) Vol 2 Num 4. -
Article: The Viruses and Virus Diseases of Cassava in Africa
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ABSTRACT: This review summarises the available information on the viruses and virus diseases of cassava in Africa. It then considers the distribution, prevalence and epidemiology of the two most important of these diseases: African cassava mosaic, which occurs in all the main cassava-growing areas, and cassava brown streak, which seems to be restricted to parts of eastern and southern Africa. The epidemiology of African cassava mosaic has been studied in few of the very diverse agro-ecological zones in which the disease occurs and there is even less information on brown streak. These are serious constraints in attempts to develop effective control measures. Information is also lacking on possible interactions between the two diseases and on their effects on the response of cassava to bacterial blight and other disease and also to arthropod pests, nematodes and weeds. This emphasizes the scope for a multi-disciplinary holistic ecological approach in any further studies aimed at developing fully integrated control measures to combat the whole range of cassava pests, diseases and weeds.African Crop Science Journal (ISSN: 1021-9730) Vol 2 Num 4. -
Article: Influence of NPK Fertiliser on Populations of the Whitefly Vector and Incidence of Cassava Mosaic Virus Disease
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ABSTRACT: The influence of NPK fertiliser on the symptoms and spread of cassava mosaic virus disease (CMD) and on populations of the whitefly vector ( Bemisia tabaci ) was investigated in Uganda using three cassava varieties: Migyera (CMD-resistant), Nase 2 (tolerant) and Ebwanatereka (highly susceptible) in 1995-96 and 1996-97 planting seasons. In each season NPK fertiliser significantly (P<0.05) increased the incidence of CMD and led to earlier infection and spread of the disease for varieties Migyera and Nase 2 than in unfertilised control plots, whereas for variety Ebwanatereka no significant differences in infection and disease spread were observed for the control and plots that received NPK application. Adult whitefly populations per shoot were increased significantly (P<0.05) by NPK fertiliser on Nase 2 and Ebwanatereka in 1995-96 and on Ebwanatereka in 1996-97, although the increases were not significantly different. Application of NPK fertiliser did not significantly influence the population of whiteflies on variety Migyera in either experiment. Similarly, NPK fertiliser application did not influence CMD symptom severity for all varieties in either season. These results indicate that NPK fertiliser application is not satisfactory strategy for facilitating the control of CMD.African Crop Science Journal (ISSN: 1021-9730) Vol 11 Num 3. -
Article: African cassava mosaic virus disease : an under-estimated and unsolved problem
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Article: Effects of African cassava mosaic geminivirus on the yield of cassava
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Article: La virologie des plantes en Afrique tropicale : les styles anglais et français
Top co-authors
Top Journals
Institutions
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2004–2008
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University of Greenwich
- Natural Resources Institute
London, ENG, United Kingdom
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2006
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Institut de recherche pour le développement
Marseille, Provence-Alpes-Cote d'Azur, France
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2000
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Consultative Group on International Agricultural Research
Washington, D. C., DC, USA
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1998
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Greenwich University
Greenwich, CT, USA
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