Tag Archives: virus

CGIAR centres and research programs combine forces to reduce the damage of banana disease in Uganda

Bananas and plantains (Musa spp.) provide a major source of food and income for over 30 million people in Eastern and Central Africa (ECA). Uganda produces an estimated 10 million tonnes annually valued at about US$550 million. Most ECA bananas are domestically consumed with the highest global per capita consumption of over 200 kg. Banana Xanthomonas Wilt (BXW), a bacterial disease, emerged in Uganda in 2001 and has since proved to have a devastating effect on banana production, with up to 100% loss if no management practices are adopted. To control the disease, farmers can adopt a package of practices, including single diseased stem removal and cleaning of tools to prevent contamination. Alternatively, resistant cultivars are under development. Several policy interventions are thus available but it is not clear which will have the greatest impact on curbing the spread of BXW while minimizing the costs.

Bioversity International, under the umbrella of the CGIAR Research Program on Roots, Tubers and Bananas (RTB), organized a workshop in Kampala, Uganda, 1–2 February 2018, to understand better the socio-economic impact of BXW spread and quantify the role of policy interventions. The goals of the workshop were to:

  1. Finalize and validate the conceptual framework describing relationships between different elements of BXW spread and its socio-economic consequences, linking different scales – from farm to country levels
  2. Finalize and validate research questions of the study
  3. Identify what data, methods and models are available and what resources are needed to fill in the missing elements
  4. Generate a framework for linking the models 
  5. Formulate scenarios for simulation modeling, which would represent possible alternative future (until 2050) developments to inform policymakers
  6. Roadmap tasks and deliverables 

The research will answer the question: What will be the socio-economic impact of BXW spread in Uganda until 2050 if there are no policy interventions, and under different interventions?

A shrivelled male bud is a symptom of Xanthomonas wilt. Credit: Bioversity International/A. Vezina

This highly complex question requires an integrated modelling approach which can be modelled to see the impact of different interventions on banana production, producers’ revenue, market prices, consumption and nutrition, and link them to costs for different actors, starting from the government and ending with farmers. To address such different areas of focus and implications at multiple scales, from the farm to (inter)national level, the research brings together a highly multidisciplinary team hailing from different CGIAR research centres, different disciplines (agronomists, economists, plant pathologists, mathematicians), different CGIAR research programs, different flagships within the CGIAR Research Program on Roots, Tubers and Bananas, together with representatives of Makerere University and the National Agricultural Research Organization of Uganda.

This innovative research links various models in order to understand the economic impact of pest and disease spread. We start with the dynamic global partial equilibrium model – IMPACT, developed by the International Food Policy Research Institute (IFPRI) with support from the CGIAR Research Program on Policies, Institutions and Markets (PIM). This is an economic simulation model for analysis of long-term agricultural markets and food security. A crop disease mapping model based on statistical analysis of survey data will be combined with a mathematical model for disease spread dynamics, in order to inform the IMPACT model about the dynamics of BXW spread and its consequences for yield loss. Additionally, we will systematically assess costs borne by different actors in the food system. 

By combining expertise from RTB research clusters on resilient crops, banana bacterial wilt, improved livelihoods at scale, foresight and impact assessment, and sustainable intensification/ diversification, and linking those with the IMPACT model, we have the potential to make innovative breakthroughs that can truly make a difference in the management of the devastating BXW disease and defend Uganda’s economic base and food security. 

Read the original article and learn more about Banana Xanthomonas Wilt on the Bioversity International website. 

This research is part of the CGIAR Research Program on Roots, Tubers and Bananas and is supported by CGIAR Fund Donors. Additional support, for the IMPACT modelling part was provided by the CGIAR Research Program on Policies, Institutions and Markets (PIM) through the Global Futures and Strategic Foresight project.

Revolutionary mobile app for monitoring crop pests and diseases

Just as the late blight epidemic wiped out potato fields in Ireland in the 19th century, crop pests and diseases still have devastating effects on smallholder farmers today – with scenarios projected to worsen under climate change.

Cassava brown streak disease is spreading westward across the African continent, and together with cassava mosaic disease, threatens the food and income security of over 30 million farmers in East and Central Africa. Likewise, banana is threated by fungal and bacterial diseases and banana bunchy top virus, while sweetpotato is faced with viruses and Alternaria fungi.

Farmers are often unable to properly identify these diseases, while researchers, plant health authorities and extension organizations lack the data to support them.

To overcome these issues, a team under the CGIAR Research Program on Roots, Tubers and Bananas (RTB), are working on a revolutionary app to accurately diagnose diseases in the field, which will be combined with SMS services to send alerts to thousands of rural farmers.

Diagnosing cassava disease in the field. Photo IITA

The team, led by David Hughes of Penn State, and James Legg of IITA – who leads RTB’s flagship project on Resilient Crops – together with scientists from CIAT, CIP and Bioversity International, are presenting their proposal as one of 12 finalists for a $US100,000 grant as part of the CGIAR Platform for Big Data in Agriculture Inspire Challenges at the Big Data in Agriculture Convention 2017 in Cali, Colombia this week.

The concept leverages three critical advances in how knowledge is communicated to the farm level: 1) the democratization of Artificial Intelligence (AI) via open access platforms like Google’s TensorFlow, 2) the miniaturization of technology allowing affordable deployment and 3) the development of massive communication and money exchange platforms like M-Pesa that allow rural extension to scale as a viable economic model enabling last mile delivery in local languages.

Painstaking field work using cameras, spectrophotometers and drones at RTB cassava field sites in coastal Tanzania and on farms in western Kenya has already generated more than 200,000 images of diseased crops to train AI algorithms.

Using many of these images, Hughes, Legg and collaborators were able to develop an AI algorithm with TensorFlow that can automatically classify five cassava diseases, and by collaborating with Google, the team have been able to develop a TensorFlow smartphone app that is currently being field-tested in Tanzania. Penn State has also developed a mobile spectrophotometer through a start-up called CROPTIX. Early results suggest it can accurately diagnose different viral diseases in the field, even if the plant looks healthy.

 “The concept leverages RTB’s global network across multiple crops for testing and scaling with national partners and the private sector in all three continents where we work. This technology will enable small-scale farmers to quickly take action and stop the spread of pests and diseases in their farms, protecting these critical sources of food and income security,” said Graham Thiele, RTB Program Director. “We are really excited about this initiative and delighted to be teaming up with Penn State,” he added.

A Tanzanian farmer examines his cassava plants for the presence of pests and disease. Photo H.Holmes/RTB

The project team has already developed linkages with the Vodafone agriculture SMS platform called DigiFarm, which positions them strategically to link digital diagnostics to large-scale rural text messaging services. The team will deliver farmer tailored SMS alerts on crop diseases and pests to 350,000 Kenyan farmers by July 2018.

Once the diagnostic and SMS systems are up and running, their impact will be determined by assessing how rapid disease diagnosis increases yield in cassava value chains in Kenya involving 28,000 farmers.

An existing platform housed by Penn State (www.plantvillage.org) will enable real time discussions of disease and pest diagnoses across the CGIAR community and with other experts to enhance SMS alerts from the DigiFarm platform.

It’s is envisaged that these innovations, initially piloted in East Africa, will provide a model that can be extended to the range of locations where RTB works, and in so doing impact the farming and livelihoods of hundreds of millions of farmers.

See more in the project flyer. 

Increasing the resilience of roots, tubers & bananas

Given its focus on the resilience of root, tuber and banana crops, Flagship Project 3 (FP3) aims to incorporate environmental, biological, ecological and economic considerations into the various ‘clusters’ – distinct projects within the flagship.

Crop resilience can be compromised in myriad ways, notes James Legg, FP3 leader and a plant virologist at the International Institute of Tropical Agriculture (IITA). Among them:

  • Biological factors: including pests, diseases and the inevitable introduction of alien invasive species into a new geographical region as a function of increased international trade and people’s global movement patterns
  • Environmental factors: ranging from drought and increased soil salinity to unexpected spikes or drops in temperature
  • Agro-ecological factors: such as the over-exploitation of land through multiple cycles of cropping, which leads to soil degradation, nutrient deficiencies and other problems
  • Social factors: T for example, population growth leading to greater pressure on agricultural land, or the impacts on shareholders of increasingly smaller farming plots
  • Factors related to changing global climate: these effects will differ greatly among crops and could include shortened life cycles and increased economic damage from major pests.

Cassava farmer examines his field infected by cassava witches’ broom disease in Cambodia. Photo G.Smith/CIAT

Across this array of threats to resilience, technology is vitally important for achieving the goals of FP3, Legg says. For example, sequencing DNA from a specific pest can help the team determine which species are present in which locations, leading to more precisely targeted control efforts.

Moreover, the ability to use new tools to diagnose a disease more quickly and cheaply goes a long way toward containing the threat it poses.

“The invasive pathogen Fusarium oxysporum fsp cubense – Tropical Race 4 – was detected for the first time on the African continent, in a single farm in Mozambique, through the use of a molecular diagnostic method using polymerase chain reaction (PCR),” Legg says. “FP3 scientists and their partners are now using these diagnostics in a containment programme that will map the geographic spread of this new pathogen prior to designing a comprehensive control strategy.”

Yellow and wilted leaves are typical symptoms of Fusarium wilt. Photo G.Blomme/Bioversity International

Sometimes, efforts to boost crop resilience occur in isolation from efforts to enhance other desirable traits. Yet that won’t always be the case: Legg observes that increasingly in Phase II, FPs will combine to “bring these two lines of work together so that improved nutritional profiles” – whose development IN orange-fleshed sweetpotato (OFSP), cassava and banana is being addressed in FP2 and FP4 – “will be combined with resistance to major biotic and abiotic threats in new varieties developed and promoted.” In fact there are multiple natural points of intersection among FP3’s focus on resilience and its sister flagships. By the same token, germplasm development work housed under FP2 will dovetail with specific clusters in FP3. In addition, FP3’s project to improve diagnosis and control using phytosanitation of banana bunchy top virus (BBTV) is being linked to other flagships to help scale up efforts to control its spread.

In theory, how long would it take for Legg and the rest of the FP3 team to ascertain if resilience has increased in a given crop? It all depends on the factors against which resilience is being gauged, he says.

For example, since FP3 covers much of RTB’s disease-management work, it might only require two or three growing seasons (ideally in different locations) to measure whether crops now display greater ability to withstand pest and disease pressures. Yet “for factors such as climate change or soil degradation, the period required may be longer,” he says.

“Much of the cross cutting thinking on resilience in FP3 is being undertaken within cluster 3.2, Sustainable Cropping Systems,” Legg continues. “Under this cluster, research is being undertaken that aims to develop resilient production systems. Since this work considers the whole system, with its diversity of crops and environments, there is an inherent complexity. This will mean that it will take several years before systems with enhanced resilience can be developed, and several more years before the robustness of those systems can be confirmed.”

Cassava farmer, Mr. Khalifa Omari Nkrumah, of Mkurangra district, Tanzania inspects his cassava plants for the presence of Cassava Brown Streak Disease. Photo H.Holmes/RTB

As resilience increases, so too can smallholders’ potential economic and social benefits. Yet Legg cautions that there’s no quick path from greater resilience to greater revenue.

“Yield increases can be converted to estimates of economic gain and increased income,” he notes. “Calculating the impact at the community level is significantly more challenging, and requires the implementation of impact studies conducted at the community level both before baseline and after the implementation of resilience-promoting activities.” Typically speaking, community level change is achieved only after a meaningful period of scaling – which is where FP5 Improved Livelihoods at Scale will engage and support.

“The key theme unifying all of the FPs is the development of productive, profitable and sustainable systems that will ensure that roots, tubers and bananas make a major contribution to sustaining and enhancing the livelihoods of the growing number of people living in the tropical parts of the developing world,” Legg says. “In all the FPs, we share a common goal, and we are working closely together to achieve that.”

This is the third in a series of blogs showcasing the new Flagship Projects of the CGIAR Research Program on Roots, Tubers and Bananas. The next edition will examine Flagship 2 on ‘Adaptive Varieties and Quality Seed‘. By Amy Rogers Nazarov

Assessing the impact of Cooperation-88 potatoes in China

Potatoes came to China in the early 1600s but were not a major crop until the 1980s. By 1993, China became the world’s largest potato producer, and in 2014, it produced 96 million metric tons – twice as much as India, the second largest producing country[i]. This significant growth in potato production highlights how important potatoes have become in China. This importance is driven by income growth and rapid changes in consumer demand.

Since early 2013, the Chinese government has refined their food security strategy and has been promoting potato as a new staple crop to improve food security and water shortages throughout the country[ii]. Because potatoes have a long storage life and use limited water in production, all while remaining a nutritious option, potato research is now a priority.

As part of the Chinese potato breeding program, several varieties have been produced to increase potato yield while reducing the impact of main biotic constraints in potato production – the most important being late blight.

One of those varieties is Cooperation-88 (C88) which was developed through a collaboration between the International Potato Center (CIP) and Yunnan Normal University (YNU), with the goal of breeding a high quality, late blight resistant variety that tastes good[iii]. In 1996, C88 was named and released as a cultivar. By 2009, it covered 186,667 hectares and was the most widely grown variety in Yunnan[iii]. C88 is now grown in four provinces: Yunnan, Sichuan, Guizghou, and Guanshi.

Current estimated adoption rates of C88 by season in Yunnan

 Season   Estimated Adoption Rate (%)
 Early Spring   27
 Late Spring   17
 Autumn   8
 Winter   56

Source: SIAC Expert Panel in Yunnan on March 10, 2015

It is evident from the high adoption rates that C88 has made an economic impact. The variety is expected to benefit adopting farmers in the form of higher yield (due to its late blight resistance property) and price, which in turn should increase farm income and household food security.

The Project

To measure the impact of C88, a collaborative effort funded by the Standing Panel on Impact Assessment with additional funding from The CGIAR Research Program on Roots, Tubers and Bananas (RTB), was undertaken by CIP, Virginia Tech (VT), and YNU. Previous studies estimated the adoption of C88 but none rigorously quantified the impact.

The study objectives are to verify previous adoption estimates of C88 in Yunnan, and determine the economic benefits C88 has had on consumers and producers in China.

A random household and a community survey conducted in Yunnan were used to gather information about potato production. The purpose of the household survey was to collect information on potato production and demographic and socioeconomic characteristics of potato-producing households. The community survey was used to verify the data from the household survey at the village level and to estimate the yields and cost of production for C88 compared to alternative potato varieties.

Junhong Qin, Research Assistant, CIP, surveys a local potato farmer.

An enumerator surveys a local potato farmer for the project.

From July to early September 2015, a research team from YNU, CIP and VT interviewed 616 farmers in 41 villages. Interviews with value chain actors, such as potato chip processors and wholesalers, were also conducted.

A First Look at the Results

When finished, this project will paint a picture of potato farmers in Yunnan and what influences their decisions to adopt potato varieties. This will inform researchers such that new varieties that meet producer needs can be developed and disseminated more efficiently. The more qualitative results from the value-chain study will also provide feedback to potato researchers and policy makers on constraints faced by farmers in C88’s value-chain.

A major constraint to the adoption of C88 that the survey uncovered is a lack of seed markets. Many farmers grow one variety until another is introduced. They do not generally purchase new seeds of the same variety. Instead, they completely replace one variety for another. As seed quality degrades, production suffers because quality seed potatoes are not available.

Farmers preferred C88 because of its high yield and high quality, which leads them to receive a higher price.

While C88 has many positive traits, the two major problems reported by farmers were decreasing yields as the seed stock ages and late maturity. Although C88 is late blight resistant, it is still affected by late blight because it matures later than other varieties and may still be in the fields as moisture appears. Farmers are beginning to replace C88 with varieties that mature earlier because late blight does not become a major concern until later in the season. However, potato processors value C88 tubers and recognize the importance of the variety to the rapidly expanding processed chip industry.

C88’s value-chain is comprised of two main markets: chip processing and fresh consumption. Medium-sized tubers go to chip processors who prefer C88 over most varieties due to its low water content, high starch, and medium sized tubers. One chip processor reported a shortage of C88 and thus, the need to resort to another variety to supplement his processing business. Larger tubers are destined to the fresh market, and mainly found in large restaurants, such as those in hotels; savvy consumers prefer C88’s taste and quality.

What’s next?

The next steps are to analyze the household and community data to supplement the qualitative findings. This will allow researchers to determine the adoption rate of C88 in Yunnan Province, identifying factors that affect farmers’ adoption decision of C88, and estimating the economic impact of C88 in China. The various research methods, mentioned above, will provide feedback to researchers on the importance of potato research to China and C88’s impact on farmers, consumers, and China.

China is also set to host the first World Congress on Root and Tuber Crops, due to take place in Nanning, Guangxi province from 18 – 22 January 2016. The Congress will bring together the world’s foremost experts in the field to share advice, review scientific progress, and identify and set priorities for future research, along with raising awareness of the global importance of root and tuber crops like potato.

This blog was contributed by Stephanie Myrick, Jeffrey Alwang and Catherine Larochelle from Virginia Tech, and Guy Hareau and Willy Pradel from the International Potato Center. 

[i] FAOSTAT. (2015). Top 20 Commodities by Country.

[ii] China Daily. (2015, January 8). Potato upgraded as new staple crop.

[iii]  Li, C., Wang, J., Chien, D. H., Chujoy, E., Song, B., & VanderZaag, P. (2011). Cooperation-88: A High Yielding, Multi-Purpose, Late Blight Resistant Cultivar Growing in Southwest China. American Journal of Potato Research.

New evidence supports integrated seed health strategy as best option for raising potato yields

Potato is the third most important food crop globally and over half of all production occurs in developing countries. However, the use of poor quality potato seed in these regions is significantly reducing yields and impacting the livelihoods of small-scale potato farmers and their families.

‘Potato seed’, or sprouted potato tubers that can be replanted, become degenerated through a buildup of pathogens and pests caused by successive cycles of propagation. Diseases can be contracted via pathogens present in the soil, air or through vectors like aphids. As potatoes are primarily propagated vegetatively, some of these diseases in the plant can be carried over to the next generation.

Typically, resource-poor small-scale farmers propagate their own potato seed from their fields or acquire them from neighbors or the local market. Research has found that these seed tubers often have poor health status, causing smaller yields and low quality potatoes that fetch lower market prices.

A farmer with his freshly harvested potatoes. Photo by N.Palmer/CIAT

A farmer holds his freshly harvested potatoes in East Africa. Photo by N.Palmer/CIAT

In industrialized countries, potato seed degeneration has largely been overcome through the establishment of certified seed systems. Farmers can purchase seeds that are tested and certified to meet a government-regulated minimum health status, helping to reduce the instance of disease.

However, attempts to establish such formal seed systems in developing countries have had limited success for numerous reasons. Many of these nations lack the infrastructure, resources, trained personnel and governmental or private sector institutions necessary to produce and regulate certified seed. Other factors including the high cost of formally certified seed, uncertain connections to markets due to fluctuating prices and other economic factors also play a role.

Recognizing the complex challenges that restrict the effectiveness of certified seed systems in developing countries, the authors of a new paper published in the journal Plant Pathology entitled, ‘Seed degeneration in potato: the need for an integrated seed health strategy to mitigate the problem in developing countries’ propose a combination of strategies to help farmers improve the quality of their potato seed, and in turn, their yields.

Seed potatoes. Photo by S.Quinn/CIP

Seed potatoes. Photo by S.Quinn/CIP

The authors argue that advocating the exclusive use of certified seed as a ‘silver bullet’ to manage degeneration in developing countries is overly simplistic. Instead they propose the adoption of an ‘integrated seed health strategy’ that is tailored to the local context. Such a strategy involves using a combination of host plant resistance and better on-farm management practices, in conjunction with strategically replacing diseased seed with certified or ‘quality-declared’ seed (when financially viable).

Such on-farm practices include ‘plant selection’ which involves visually identifying and selecting only symptomless plants as the seed source for the next season, and ‘roguing’ which is the process of identifying, removing and destroying abnormal plants that show symptoms of disease. These methods are both effective and low cost, however they do require farmer training in symptom recognition. Other management strategies such as using straw mulching to affect aphid flight activity also hold great promise for resource-poor farmers.

To aid the implementation of integrated seed health strategies, the authors call for further research in areas including understanding the interrelationships between risk factors affecting potato seed degeneration and cultivar resistance to degenerative diseases. In this regard, a globally collaborative study is currently underway as a part of the CGIAR Research Program on Roots, Tubers and Bananas (RTB). One of the objectives of this study is to develop models to predict degeneration that include the effects of host resistance and environmental risk factors.

The research for the paper was funded by RTB, the CGIAR Research Program on Climate Change, Agriculture and Food Security, the Kansas Agricultural Experiment Station and the Scottish Government’s RESAS division. In conjunction with the McKnight Foundation for the projects ‘Strengthening systems for native potato seed in Bolivia, Ecuador, and Peru’ and ‘Understanding potato seed degeneration in Ecuador’, Indian Council of Agricultural Research, and USDA Specialty Crop Research Initiative Grant.

Mosaic and Brown Streak Disease in Cassava

Scientists alarmed by the rapid spread of brown streak disease in cassava, a crop that sustains 300 million Africans

World’s cassava experts to wage war against cassava viruses;
Introduction into Nigeria, the largest cassava producer in the world, could result in drastic food shortages in this part of Africa

Mosaic and Brown Streak Disease in Cassava

Mosaic and Brown Streak Disease in Cassava

BELLAGIO, ITALY (6 MAY 2013)— Cassava experts are reporting new outbreaks and the increased spread of Cassava Brown Streak Disease or CBSD, warning that the rapidly proliferating plant virus could cause a 50 percent drop in production of a crop that provides a significant source of food and income for 300 million Africans.

The “pandemic” of CBSD now underway is particularly worrisome because agriculture experts have been looking to the otherwise resilient cassava plant—which also is used to produce starch, flour, biofuel and even beer—as the perfect crop for helping to feed a continent where growing conditions in many regions are deteriorating in the face of climate change.

“Cassava is already incredibly important for Africa and is poised to play an even bigger role in the future, which is why we need to move quickly to contain and eliminate this plague,” said Claude Fauquet, a scientist at the International Center for Tropical Agriculture (known by its Spanish acronym CIAT) who heads the Global Cassava Partnership for the 21st Century (GCP21). “We are particularly concerned that the disease could spread to West Africa and particularly Nigeria—the world’s largest producer and consumer of cassava—because Nigeria would provide a gateway for an invasion of West Africa where about 150 million people depend on the crop.”

Fauquet and his colleagues in the GCP21—an alliance of scientists, developers, donors and industry representatives—are gathering at the Rockefeller Foundation Bellagio Center in Italy this week for a conference dedicated to “declaring war on cassava viruses in Africa.” For Graham Thiele, Director of the CGIAR Research Program on Roots, Tubers and Bananas (RTB), supporting such an initiative is exactly what RTB is about: “We can only tackle big issues by joining forces and GCP21 is an ambitious convening mechanism to address with one of the most important constraints faced by cassava producers”.

A “Silent Killer” Emerges: CBSD on Warpath from East to West

First identified in 1935 in East Africa and little-known until about ten years ago, CBSD has emerged as the most serious threat among the various cassava viruses. Infections can claim 100 percent of a farmer’s harvest without the farmer’s knowledge. The leaves of infected plants can look healthy even as the roots, cassava’s most prized asset, are being ravaged underground. The tell-tale signs of the disease are brown streaks in the root’s flesh that, when healthy, provide a rich source of dietary carbohydrates and industrial starchy products.

There have been recent reports of new outbreaks in the Democratic Republic of the Congo—the world’s third largest cassava producer—and Angola, where production has boomed in recent years. The spread of the disease to West Africa and particularly Nigeria is a major cause for concern, experts say, because the country now produces 50 million tons of cassava each year and has made a big bet on cassava for its agricultural and industrial development in the near future.

Nigeria is the first African country to massively invest in the potential of cassava to meet the rapidly growing global demand for industrial starches, which are used in everything from food products to textiles, plywood and paper. Nigeria hopes to mimic the success of countries in Southeast Asia, where a cassava-driven starch industry now generates US$5 billion per year and employs millions of smallholder farmers and numerous small-scale processors.

CMD—a Scourge for Cassava on the African Continent

Brown Streak Disease

Brown Streak Disease

Scientists at the conference will also consider options for dealing with another devastating virus—the Cassava Mosaic Disease (CMD). CMD has plagued the whole African continent for over a century, each year removing a minimum of 50 million tons of cassava from the harvest.

The disease is caused by several viruses and the African continent witnessed several major CMD epidemics over the past decades, the most recent and devastating pandemic occurred the 1990s in East and Central Africa. Great success was achieved in combating the CMD pandemic through developing and disseminating varieties that were resistant to CMD. In fact, by the mid-2000s, half of all cassava farmers were benefiting from these varieties in large parts of East and Central Africa. But by a cruel twist of nature, both improved and local varieties all succumbed to the ‘new’ pandemic of CBSD.

Unexpected Plot Twist: Whiteflies Ambush a Climate-Resilient Crop

Interest in cassava has intensified across Africa as rising temperatures and shifting rainfall patterns caused by climate change threaten the future viability of food staples such as maize and wheat. Cassava has been called the “Rambo root” for its extraordinary ability to survive high temperatures and tolerate poor soils. But rising temperatures now pose a threat to cassava because they appear to be one of several factors causing an explosion in whiteflies, which carry the viruses that cause CMD and CBSD and pass it along as they feed on the plant’s sap.

Compounding the effects of rising temperatures, scientists also think that genetic changes have led to the emergence of “super” whiteflies. This toxic mix of circumstances affecting a tiny fly threatens to shoot down the “Rambo root,” bringing the misery of food insecurity to vast swathes of Africa.

“We used to see only three or four whiteflies per plant; now we’re seeing thousands,” said James Legg, a leading cassava expert at the International Institute of Tropical Agriculture (IITA). “You literally have a situation where human beings are competing for food—with whiteflies.”

Farmers also help spread the disease by planting new fields with infected stem cuttings. Scientists note that while it would take several years for the disease to spread across the continent via whiteflies alone, infected stem cuttings could spark outbreaks in new areas overnight.

Experts to Develop Plan to Stop Viruses in their Tracks

At the Italy meeting, experts will discuss a variety of tactics for combating virus diseases, such as developing more disease-resistant varieties like those recently released in Tanzania. Efforts to breed high-yielding disease-resistant plants suitable for Africa’s various growing regions will involve going to South America, where cassava originated, and working with scientists to mine the cassava gene bank at CIAT in Colombia—the biggest repository of cassava cultivars in the world.

The expert team will also discuss a more ambitious plan: how to eradicate cassava viruses altogether. The aim will be to develop a bold regional strategy that will gradually, step-by-step, village-by-village, replace farmers’ existing infested cassava plants with virus-free planting material of the best and most resistant available cultivars. Approaches will include new molecular breeding and genetic engineering technologies to speed up the selection and production of CMD and CBSD resistant cassava cultivars more appealing to farmers.

There also will be discussions about cost-effective and environmentally sustainable ways to control whiteflies, as well as proposals for new surveillance systems that can better track and stop the disease from spreading and new research into the potential threat African cassava producers face from the introduction of new diseases currently found outside the continent.

“It’s time for the world to recalibrate its scientific priorities,” Fauquet said. “More than any other crop, cassava has the greatest potential to reduce hunger and poverty in Africa, but CBSD and other viruses are crippling yields. We need to treat CBSD and other destructive viruses like the smallpox of cassava—formidable diseases, but threats we can eradicate if everyone pulls together.”


Founded in 2003, the Global Cassava Partnership for the 21st Century (GCP21) is a not-for-profit international alliance of 45 organizations and coordinated by Claude Fauquet and Joe Tohme of the International Center for Tropical Agriculture (CIAT). It aims to fill gaps in cassava research and development in order to unlock the potential of cassava for improving food security and also increasing incomes of poor farmers through work to develop industrial products from cassava. GCP21 is providing updated information regarding the crop, the scientists working on cassava and cassava R&D projects in the world.

The International Center for Tropical Agriculture (CIAT) and the International Institute of Tropical Agriculture (IITA) are nonprofit research-for-development organizations and members of the CGIAR Consortium. Along with Bioversity and the International Potato Center, they participate in the CGIAR Research Program on Roots, Tubers and Bananas (RTB), an initiative bringing together the research synergies and resources of centers and partners to tap the underutilized potential of root, tuber, and banana crops to improve food security, nutrition, and livelihoods.

Additional Institutions attending the Third Strategic Meeting of the Global Cassava Partnership for the 21st Century, Bellagio, Italy: CGIAR Fund; Food and Agriculture Organization of the United Nations (FAO); International Fund for Agricultural Development (IFAD); World Bank; the African Development Bank (AfDB); United States Agency for International Development (USAID); Bill & Melinda Gates Foundation; Syngenta Foundation; Catholic Relief Services (CRS); Kenya Agricultural Research Institute (KARI); Mikocheni Agricultural Research Institute (MARI), Tanzania; DSMZ; Natural Resources Institute (NRI); Tel Aviv University; Institute of Resources Assesssment (IRA), Tanzania; National Agricultral Crops Resources Research Institute (NACRRI), Uganda.