Developing clean seed systems for cassava

James Legg,

Cassava stems for future crop. Photo by L. Kumar, IITA.
Cassava stems for future crop. Photo by L. Kumar, IITA.

Cassava is one of those crops that uses part of the plant for propagation. It is very convenient to use vegetative material from a previous crop to plant a new one. This is one of the beauties of vegetatively propagated crops. However, this convenience comes at a price. The use of planting material from a previous generation to establish the next provides an easy way for disease-causing pathogens, particularly viruses, to pass directly from one plant generation to another. So, while they offer convenience, vegetatively-propagated crops are often more widely affected by pathogens than those planted in the form of true seeds.

In Africa, cassava is the most widely cultivated of the vegetatively-propagated crops, being grown on more than 12 million ha across the continent. The exotic pest introductions, cassava mealybug and cassava green mite, caused great damage to Africa’s cassava crop in the 1980s and 1990s, but both have been effectively managed through the implementation of a classical biological control program.

The fungal diseases, cassava bacterial blight (Xanthomonas axonopodis pv. manihotis) and cassava anthracnose (Colletotrichum gloeosporioides f. sp. manihotis) are locally important. The greatest current constraints to cassava production, however, are the virus diseases, cassava mosaic disease (CMD) caused by cassava mosaic geminiviruses (CMGs) and cassava brown streak disease (CBSD) caused by cassava brown streak viruses (CBSVs), which together cause crop losses worth more than US$1 billion annually.

One of the most important approaches to controlling these virus diseases, as well as other pathogens of cassava, is through the avoidance of infection. This can be achieved by starting out with pathogen-tested plants, and then bulking the planting material through a series of quality controlled multiplication steps. Although it sounds very simple, this can be difficult to achieve in practice.

Pathogen testing requires well-equipped laboratories run by adequately trained staff. Quality management in the field requires extensive grassroots knowledge of disease symptoms and the involvement of an appropriately trained and resourced national plant protection organization. In many parts of sub-Saharan Africa, capacity for these functions remains insufficient to meet the demands.

IITA and its partners have made significant progress in developing and implementing new systems to maintain the health of cassava through seed systems. For instance, through the Great Lakes Cassava Initiative (GLCI), a multi-partnered project implemented from 2007 to the present in Burundi, Democratic Republic of Congo, Kenya, Rwanda, Tanzania, and Uganda, a rigorous system has been put in place to assure the health of cassava planting material. This has been particularly important in view of the rapid recent spread of a devastating pandemic of CBSD in East Africa.

Healthy cassava plant. Photo by IITA.
Healthy cassava plant. Photo by IITA.

The key components of the quality and health management system are as follows: Primary (centralized seed production sites) managed by researchers or qualified seed producers, secondary, and tertiary multiplication sites (usually in farmers’ fields) are all assessed, at least once in a year, using the Quality Management Protocol (QMP). This sets out quality levels, primarily in terms of disease and pest incidence and material quality that must be met if the field is to “pass”.

The QMP standards for CMD and CBSD incidences ascertained by diagnostic tests are <10% for primary and secondary sites and <20% for tertiary sites in endemic areas. Planting materials from fields that fail to meet QMP standards are not distributed or used for further multiplication, although the tuberous roots can be used by the growers for consumption. Fields that meet the QMP standard and test negative for CBSVs are approved for more widespread dissemination.

This is the first time that this level of rigor has been applied to maintaining the health of cassava through multiplication programs in sub-Saharan Africa. It has been invaluable in assuring the health of the planting material provided to more than half a million beneficiaries in six countries, and provides an important model for other current and future cassava development programs.

Much remains to be done before such an approach can be used in a more sustainable way. Most importantly, basic capacity needs to be strengthened in most countries. Key elements of this include the laboratory and human capacity for virus indexing, as well as the knowledge of QMP and the capacity of the national plant quarantine organization to monitor cassava seed systems.

In addition, the management of cassava diseases could be greatly enhanced by the establishment of isolated nuclear multiplication sites planted with virus-tested cassava plantlets derived from tissue culture, as well as by raising awareness among growers about the importance of establishing the next crop with healthy planting material.

A long-term goal, as the commercial value of cassava increases, will be to provide a mechanism through which planting material certified through the QMP attracts a price premium. Creating added value is certain to be the key to the future development of clean seed systems for cassava in Africa. IITA and its partners are strongly committed to reaching this goal.

Battling cassava disease

The cassava brown streak disease continues to threaten the food security and livelihoods of over 200 million people in East Africa. It causes greater economic damage than the mosaic disease as it destroys the more valuable part of the crop—the roots.

The disease had previously been confined to lowland coastal areas in East Africa, but the new outbreak has spread rapidly to the high altitude regions (over 3000 feet above sea level) of Uganda, Kenya, and Tanzania around the shores of Lake Victoria.

Almost three-quarters of the population of Zanzibar rely on agriculture for food and income, with cassava being the second most important staple after rice. Over 90% of the island’s subsistence farmers grow cassava.

Zanzibar scientists and IITA, with support from the Rockefeller Foundation and other partners, bred new cassava varieties to combat the brown streak menace. In 2007, the national agricultural system released four tolerant varieties that yield twice as much as the local varieties while satisfying local preferences such as taste and cooking texture. They have been welcomed by the farmers.

Currently, the challenge is to get enough planting materials to meet the demand. Only 10,000 cassava farmers out of almost a million on the island are growing the improved varieties. The government, IITA, and several development partners and donors such as the Alliance for a Green Revolution in Africa have been engaged in efforts to rapidly multiply these varieties to ensure that they are available to as many farmers in the shortest possible time.

Efforts are also under way to identify suitable varieties for neighboring countries and in the mid-altitude zones of Tanzania. Already, more than 15 varieties have been identified in Uganda and Tanzania that show acceptable tolerance levels even under the harshest conditions of disease pressure. They are expected to be released in a year or two after further testing.

Cassava: improving sustainability of farming systems

Anneke Fermont,

Throughout Africa populations are growing fast and pressure on land is steadily increasing. To maintain productivity, farmers are constantly adapting their management of natural resources. Farming systems are thus changing from ”slash and burn systems” to ”natural fallow” systems into ”continuous cropping” systems without external inputs and ultimately into more ”intensive” systems using agricultural inputs.

Pauline Auma of Busia district, western Kenya, proudly shows her cassava harvest. Photo by  A. Fermont, IITA.
Pauline Auma of Busia district, western Kenya, proudly shows her cassava harvest. Photo by A. Fermont, IITA.

Cassava-maize systems in East Africa
A principal crop in Africa’s farming systems is cassava, with a total production that has quadrupled in the last five decades to about 118 million t/year. Cassava is a major crop in East Africa, where it is often produced together with maize by smallholder farmers. Such cassava–maize-based systems are found around Lake Victoria and in Burundi, Rwanda, and eastern DR Congo. Apart from being dominated by cassava and maize (on average one-third of cropped land is planted with cassava and one-quarter with maize) these systems have a high self-sufficiency in food. Sixty percent of all households sell cassava and maize; each crop generates an average of US$90 per year.

Due to its widely varying levels of land pressure, this region allows an interesting study of natural resource management and opportunities to improve both the productivity and the sustainability of cassava-based farming systems.

Cassava is widely grown in East Africa today, but this is a recent development. Only three decades ago cassava production was limited to the odd corner in farms as enforcement of its production during colonial times had given the crop a very bad image. The remarkable change in the importance of cassava has been driven by sharply increasing land pressure. No longer having the land available to restore soil fertility through natural fallows, farmers replaced fallows with cassava.

Does cassava improve soil fertility?
Jacinta Ouma, a farmer in Teso district, western Kenya, explains: “Cassava drops its leaves on the soil while it grows. This improves the soil, so if I plant maize after cassava it grows better.” Jacinta is not alone in this belief. A similar practice, known as jachère manioc or ‘cassava fallow’, exists in West Africa.

Almost 90% of farmers interviewed in Uganda and Kenya had the same opinion. Farm surveys in Uganda and Kenya showed that farmers plant cassava on all soil types to maintain soil fertility. If land pressure increases and soils consequently become more acidic (pH <5.8) and deficient in phosphorus (P) (available P <4–5 mg/kg), farmers increasingly plant cassava in the poorest fields in their farm. In Siaya district, western Kenya, with nearly 400 people/km2, farmers planted nearly twice as much cassava on infertile soils than on fertile soils.

Women in Teso district, western Kenya, peel cassava for eating. Photo by A. Fermont, IITA.
Women in Teso district, western Kenya, peel cassava for eating. Photo by A. Fermont, IITA.

Modeling to substantiate farmer claims
To understand farmers’ observations, we used a modeling approach. Our results suggest that planting maize on an infertile soil will result in slowly declining levels of soil organic matter, while planting cassava will slowly increase soil organic matter over time. The difference is explained by the fact that cassava grows much better than maize on infertile soils. The large amounts of easily available nitrogen (N) in its crop residues likely give cassava its reputation as a soil improver.

The model estimated that cassava returns about four times more N to the soil than maize. Through its deep rooting system and its association with mycorrhizae, cassava can pump up nutrients from the subsoil and absorb nutrients from less easily accessible pools. Nutrients from its N-rich litterfall are then redistributed to more labile pools in the topsoil.

But all is not sunshine and roses. Continuous cropping systems without external nutrient inputs deplete the soil’s nutrient pool. On the highly weathered soils found in large parts of Africa, this will unavoidably result in nutrient limitation and declining crop yields. In East Africa, N and P limitations for cereal crops are widely documented. A series of field trials with over 100 farmers demonstrated that cassava production is often limited by N and P, and commonly by potassium (K).

Cassava grows better on good soils
Cassava is known for its ability to produce fair yields where other crops fail. This has led many to believe that soil fertility is not important in cassava production. Our field trials show that this is a misconception. On the contrary, using improved varieties but no fertilizer, low soil fertility was the principal constraint to production and caused farmers an average loss of 6.7 t/ ha with respect to an attainable yield of 27 t/ha. Drought caused a loss of 5.4 t/ha and poor weed control 5.0 t/ha, whereas pests and diseases caused an average loss of 3.8 t/ha.

The farm surveys showed that Kenyan and Ugandan farmers harvested on average between 7 and 10 t/ha using farmer practices. This is far below the maximum yield of 35 t/ha that was observed during the two-year on-farm fertilizer trials and clearly shows the potential for improving yields.

The field of Nikirima Arajabu in Iganga district, Uganda, shows a very strong response to NPK fertilizer. Photo by A. Fermont, IITA.
The field of Nikirima Arajabu in Iganga district, Uganda, shows a very strong response to NPK fertilizer. Photo by A. Fermont, IITA.

Using an integrated management package that consisted of an improved genotype, recommended planting practices and NPK fertilizer, average yields in farmers’ fields more than doubled from 8.6 to 20.8 t/ha. About 30% of the yield increase was due to the use of improved genotypes, while a whopping 60% was the result of fertilizer use. These findings reinforce the idea that soil fertility/nutrient availability is a principal production constraint for cassava.

Options to improve system sustainability
Though fertilizer use may be the easiest way to improve cassava productivity and improve system sustainability, high prices limit the adoption of fertilizers, unless strong markets develop. Farmers have, however, other options to improve cassava productivity, increase nutrient availability, and reduce nutrient losses within their farming system. These include: (1) better weed control and drought avoidance strategies; (2) improving cassava’s efficiency as a soil fertility improver; (3) returning cassava stems to the field after harvest to reduce nutrient losses; and (4) planting cassava in rotation/intercrop with (cash) crops that receive manure/fertilizer.

Dealing with the challenges from increasing land pressure and related sustainability issues while substantially improving crop yields requires R4D teams with a strong interdisciplinary character. African farmers have shown great resourcefulness in maintaining system productivity by introducing cassava as a soil fertility improver. Now, IITA and its partners have the challenge to come up with innovative strategies to maintain or further improve system sustainability and crop productivity in increasingly stressed farming systems.

Safeguarding local varieties ensures food security

Cassava pile after harvest. Photo by IITA.
Cassava pile after harvest. Photo by IITA.

Cassava is a food security crop to more than 600 million people in the developing world, providing incomes to resource-poor farmers, improving their livelihoods, and serving as a buffer against food crises.

The strategic importance of cassava, however, is being threatened, especially in Africa, as local varieties are in danger of disappearing because of genetic erosion and other human and natural factors.

“In Guinea, for instance, about seven local cassava varieties are fast disappearing. This is risky, especially for cassava since it is a clonal crop,” according to Paul Ilona, IITA Senior International Trials Manager. Clonal crops are those propagated through cuttings or other plant parts, not by seeds.

Genetic erosion is a process whereby the already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die out without getting a chance to breed within their endangered low population.

Both local and improved cassava varieties alike create a robust gene pool, offering choices for breeders in future breeding programs. However, the loss of genes from the extinction of some local varieties could limit future improvement programs. The endangered varieties may hold key traits that could offer possible solutions to hunger and poverty in the future.

Woman selling cassava, local market, Nigeria. Photo by IITA.
Woman selling cassava, local market, Nigeria. Photo by IITA.

To prevent the genetic erosion of cassava, IITA and the Institut de Recherche Agronomique de Guinée (IRAG) have stepped up efforts to save native African varieties with the collection of 73 local varieties from Guinea, West Africa.

These varieties are now conserved under ex situ conditions at IITA’s Genetic Resources Center (GRC) in Ibadan, Nigeria. They form part of a collection to safeguard the continent’s plant genetic resources. The collecting mission in that West African country last year was funded by the Global Crop Diversity Trust (GCDT), IRAG-Guinea, and IITA.

“The conservation of local varieties provides hope for future cassava breeding programs and helps to guarantee food security in Africa,” says Dominique Dumet, GRC Head and coordinator of the collecting mission.

Ilona says the loss of native cassava varieties might limit the number of genes available for breeders to work with. “For breeders, any time we lose (crop) genes, it hurts. That is why the conservation of local cassava varieties at GRC is important to us,” he says.

Apart from cassava, the IITA-GRC holds over 25,000 accessions of major African food crops, including cowpea, yam, soybean, bambara nut, maize, and plantain/banana. IITA shares these accessions without restriction for use in research for food and agriculture.

The collecting mission makes Guinea the fourth country, after Angola, Togo, and Bénin, to allow IITA to collect and share their germplasm with other countries, since the International Treaty on Plant Genetic Resources for Food and Agriculture went into force in June 2004.

A tale of an African farmer

Farmer Baba Alphonse, northern Benin
Farmer Baba Alphonse, northern Benin

Sixty-year old farmer Alphonse Ogoule-Okpe of Ogoukpate Village, about 40 km from Porto Novo in northern Bénin, had all but abandoned cassava and maize farming.

Many years ago, insects (mealybug and cassava green mite) and diseases (such as blight) had attacked his cassava crops and “Baba” Alphonse and many like him in his village were hit hard because of the low yields and loss of a food and cash crop. The problem was compounded by the poor soil conditions in the fields.

During a visit to the small village by IITA scientists who distributed planting materials of improved IITA cassava varieties, Baba Alphonse said, “I would be happy if the problem with these insects and diseases will be over. Thanks to IITA, I can plant a new variety that is resistant to the problem pests.”

Unknown to farmer Alphonse, a few kilometers away from his farm was where the predator of the cassava green mite, T. aripo, was first released in Benin by IITA—way back in 1993. That—and his use of the new varieties from IITA would help ensure better cassava harvests for his family and the community.

Dual-resistance cassava

IITA scientists are a step closer to making a breakthrough in developing cassava that is resistant to both the cassava brown streak disease (CBSD) and the cassava mosaic disease (CMD) in Eastern and Central Africa. The two diseases are the biggest threats to cassava production in the region putting at risk the food security and livelihoods of over 200 million people.

According to Edward Kanju, IITA cassava breeder, 14 types of the crop under research are very promising. Kanju’s team had just harvested an advanced trial of such cassava in Uganda.

This is the fourth year of trials for dual-resistance cassava for the mid-altitudes in Uganda. The trials are being conducted at Mukono, near Kampala, an area regarded as a hot spot for CBSD and CMD. The breeding work started with over 5,000 true seeds of parents with tolerance to CBSD from Tanzania for crossing with IITA varieties that are resistant to CMD.

Farmers have also been involved in the selection process to ensure that the varieties meet their preferences on cooking, taste, texture, and yield. Breeding for dual-resistance cassava is also being conducted in Tanzania and DR Congo.

Farmers keen on GM crops

The debate rages about the role of genetically modified (GM) crops in ensuring food security in sub-Saharan Africa, yet the level of awareness and basic understanding of GM crops remains low among small-scale farmers in Tanzania, a study reveals.

Researcher in cassava field
Researcher in cassava field

The study, conducted recently by IITA with the Africa College of the University of Leeds, assessed the understanding and attitudes of local farmers towards GM crops, using disease-resistant cassava as an example. It was carried out in three districts in Tanzania where cassava is an important staple crop with the Mikocheni Agricultural Research Institute and the Tanzanian Commission for Science and Technology.

The study team had to overcome difficulties of explaining GM crops in Swahili to Tanzanian farmers. They reported that the majority of the farmers interviewed said that they had never heard of GM crops. The farmers asked if these new crops were similar to hybrids and whether or not they would look and taste like current crops, or grow differently from them.

The study also found that the level of awareness was equally low among the district agricultural extension officers and relevant local district employees. Farmers look up to these officials for information and guidance.

However, the majority of the farmers were keen to increase their knowledge. They were also more interested in the potential of these crops to increase their productivity than concerned about any potential middle- to long-term risks associated with GM crop use.

Dr Caroline Herron, former IITA virologist involved in the research, said that it was clear from the study that there is a need to increase the knowledge of farmers on the pros and cons of GM crops to enable them to participate fully in the debate.

“It is important for the scientific community to raise the awareness levels of farmers by providing accurate and objective information so that they can make informed and autonomous decisions on the potential of GM crops in their agricultural practice,” she said. “The tendency of farmers to focus on short-term gains in productivity should not prevent the potential middle- and long-term risks being fully explained to them to allow them to make a clear judgment.”

Cassava plant. Photo by IITA
Cassava plant. Photo by IITA
According to the study, one barrier to raising awareness about GM crops in the country is the lack of a specialized vocabulary in Swahili for GM. The study recommends that appropriate Swahili terminology to facilitate better understanding should be developed before any campaign is launched to create awareness about GM crops.

The study further recommends that any potential trial for GM crops should be conducted in close consultation with government bodies, backed by a biosafety framework that aims at preventing any potential harm resulting from their use.

Tanzania has made good progress in developing such a framework. The country is a signatory to the Cartagena protocol that outlines the minimum standards of biosafety regulations that must be adopted by all the signatories. More significantly, the country’s biosafety framework was recently approved by the Cabinet after a lengthy consultation process.

Tanzanian scientists and IITA are working on developing GM cassava varieties that are resistant to both cassava mosaic disease and cassava brown streak disease. If they are successful, these crops could, in the future, be used to enhance the resistance of existing local varieties to increase the country’s food security.

When the issue of safety was raised, many of the participants placed their confidence on the government’s rules and regulations, which, they felt, would have been followed prior to the development of any GM crop.

The survey also identified concerns that farmers wanted addressed before participating in any GM crop trial. Farmers need unbiased information about the crops, preferably from scientists who developed them. The involvement of scientists in all stages of the trials—from ground preparation to planting to harvesting—was also very important.

Cassava pile
Cassava pile

The farmers also had confidence that the government would put in place strict rules and regulations that would be followed by both government entities and scientists in the development and trial of these crops. Some of the respondents stated that they would be seriously concerned if there were no such regulations in place and that this would prevent them from taking part in any trial.

During the trials, the farmers said that they would look not only at the crop yields but also their growth pattern, resistance to pests and diseases, and the labor required to care for the new varieties during the growing season. The taste of the new variety was also considered important by farmers who sold their surplus crop.

When asked whether they would eat the GM crops, they said that the involvement of scientists and the government in GM crop development would greatly increase their confidence to do so. According to one respondent in Bagamoyo: “…because of the way these crops are made, I would be worried about eating them unless scientists were involved in the trials and they ate the crops with me. This would show me that they believed they were safe.”

Editor’s note: The work on GM crops in Tanzania is at a very early stage and no GM cassava has been developed yet. So far, all the disease-resistant cassava varieties under trial have been developed through conventional breeding.

USAID project

Cassava plant. Photo by IITA
Cassava plant. Photo by IITA
A USAID-funded project seeks to further increase cassava production in farmers’ fields by 30% in seven sub-Saharan African countries.

The project is called “Unleashing the Power of Cassava in response to the food price crisis (UPoCA).” It aims to maximize the use of cassava to address food price crises in Nigeria, DR Congo, Ghana, Malawi, Mozambique, Sierra Leone, and Tanzania. IITA and its national partners across the seven countries will implement the US$5.3 million project.

Dr Braima James, Project Manager, said that the primary focus of the project was to expand and sustain on-farm productivity and the profitability of cassava.

Cassava procesing in Nigeria. Photo by IITA
Cassava procesing in Nigeria. Photo by IITA
““This will be achieved through the distribution of elite varieties and related inputs; dissemination of appropriate integrated crop management techniques to ensure at least 30% increase in root yields; and the promotion of entrepreneurship in cassava planting material supply.

About 267,000 farmers are expected to benefit from the project,” Dr Richardson Okechukwu, Assistant Project Manager, says. “The beneficiary-farmers are currently harvesting 7–12 t/ha across the seven countries but the project aims to raise yields to 12–30 t/ha.”

Growing cassava in cold Denmark

Kirsten Jørgensen,, and Birger Lindberg Møller,

cassava1Cassava, that tropical tuber that is a staple to millions in sub-Saharan Africa, is being grown in freezing Denmark—at the University of Copenhagen. The precious plants are grown in the greenhouse during the dark winter days when the snow is lying on the roof.

The crop has been a prime focus of the University’s research because of its importance as a food security crop and commodity in economic development. It has a high content of cyanogenic glucosides, toxic substances which may constitute a nutritional problem in regions where cassava is the dominant or sole staple food. During processing, cyanogenic glucosides are converted into cyanohydrins, ketones, and hydrogen cyanide. These are all toxic and should not be consumed in excessive amounts.

Cyanogenic glucosides are an ancient group of bioactive natural products present in crop plants, forage plants, and important trees. More than 3,000 plant species are cyanogenic, including cassava, apricot, cherry, clover, flax, barley, sorghum, wheat, bamboo, eucalypt, and poplar. We study most of these plant species to understand these compounds in terms of their synthesis, turnover and regulation, and their biological function. In these studies, we use model plants such as Lotus japonicus. Lotus contains linamarin and lotaustralin, the very same cyanogenic glucosides found in cassava. The genome sequence of Lotus has been sequenced, and the use of transgenic model plants is a key tool in our studies.

Our laboratory was a world-first in isolating all three genes for cyanogenic glucoside synthesis. This work was done in sorghum. We were also a world-first in isolating the genes responsible for cyanogenic glucosides synthesis in cassava.

Embryo culture of Kibaha. Photo by K. Jørgensen
Embryo culture of Kibaha. Photo by K. Jørgensen

Our research aims to control the level of cyanogenic glucosides in different parts of the cassava plant. It involves understanding the regulation of the biosynthetic genes and the turnover and transport processes. We use tools such as the relevant omics platforms for these studies, including metabolomics where we use high-pressure liquid chromatography and mass spectrometry to determine the constituents found in the different cassava tissues as a result of environmental challenges. A second important tool is transcriptomics. In collaboration with IITA researchers, such as Dr Ivan Ingelbrecht, we have designed a cassava DNA chip that allows us to monitor the profile of gene expression and how these profile changes for individual genes respond to plant development, nutritional status, and environmental challenges.

In the long term, we want to produce a virtual model of the cassava plant that would enable us to predict responses during growth and development, and to environmental stimuli. In these studies, changes in cyanogenic glucoside content, in the levels of the enzymes and genes controlling their synthesis, breakdown, and transport are given special attention.

Our studies will provide information on the level of natural variation from one plant to another in terms of interesting characteristics. To facilitate identification of individual plants with interesting properties, high throughput screening technologies have also been implemented. Cassava is a tetraalloploid plant. This makes traditional breeding very time consuming and complicated. The development of transgenic approaches where multiple gene copies may be “knocked out” in a single step offers great opportunities to develop varieties with an optimal content and distribution of cyanogenic glucosides.

Progress in cassava research is slow, because few research groups in the world are working on cassava. Typically, the tool boxes successfully used in wheat, maize, and rice breeding are not available in cassava. This makes breeding of new varieties cumbersome and time-consuming because many of the techniques have to be set up from scratch. One such example is the development of a transformation protocol for cassava that would enable us to knock out or insert new genes in elite cassava cultivars.

Transgenic shoots from TME12. Photo by K. Jørgensen
Transgenic shoots from TME12. Photo by K. Jørgensen

We have devoted a lot of effort to develop such a transformation system. This includes tissue culture work to establish protocols enabling us to produce embryogenic cultures and to regenerate plantlets from these. Likewise, reliable procedures for Agrobacterium-mediated gene transfer for elite cultivars had to be optimized. In this research we took advantage of the pioneering work on cassava transformation carried out at the Swiss Federal Institute of Technology (ETH) in Zürich. The system we now use is robust and we are able to transform elite lines from IITA that are high yielding and that have optimal resistance to disease and pest attack. Our transformation technology has been transferred to IITA. In 2007, we also transferred the technology to obtain cassava transformants to the Danforth Plant Science Centre, USA.

It is important to select the optimal cassava lines for our research. We want to produce cassava lines appropriate for end-users. There is not much value in engineering interesting agronomical traits into lines that have no value to the end users, i.e., the farmers and consumers. This is yet another example where close collaboration with IITA researchers has greatly benefited us. Collaboration with IITA helped us to focus our work on agriculturally important lines.

In the initial phase of our work to reduce cyanogenic glucoside synthesis, we used constitutive promoters such as that from the 35S cauliflower mosaic virus. We have now shifted our focus to using native cassava promoters that more efficiently target the cells in the tubers where, for example, synthesis of cyanogenic glucosides takes place, thus providing better control. The content of cyanogenic glucosides varies among vegetatively propagated and thus genetically identical plantlets. Accordingly, multiple tests at different growth stages have to be carried out to determine the degree of downregulation (reduction) of cyanogenic glucoside synthesis. This makes the procedure to find the right lines time-consuming.

The protein content in current elite cassava cultivars is very low partly perhaps because of the continued breeding for high starch yield. In the past, breeding for high protein content would be at least partly in vain because a significant proportion of the protein is lost anyway during processing when the cyanogenic glucosides and their toxic degradation products are removed to provide food safe for consumption.

Using molecular breeding, there are several ways to achieve transgenic lines with enhanced protein levels in the tubers. One way is to identify specific storage proteins from wild cassava varieties that exhibit a high content of essential amino acids, such as methionine and lysine, and then express these nutritionally beneficial proteins in the elite lines. Another way would be to use storage proteins from other known species, such as patatin from potato. We are currently transforming African elite lines with constructs encoding patatin that will be incorporated into the starch grains in the cassava tuber.

Transgenic acyanogenic cassava (TME12) in greenhouse. Photo by K. Jørgensen
Transgenic acyanogenic cassava (TME12) in greenhouse. Photo by K. Jørgensen

The original focus on the molecular breeding of elite cassava cultivars with a controlled and reduced content of cyanogenic glucosides and a higher protein content has recently been expanded to incorporate varieties carrying yellow tubers. These have increased levels of carotenoids that are precursors of vitamin A. IITA provided the cassava lines with high carotenoid content obtained by classical breeding.

The long-term aim of our research is to improve the nutritional value of cassava tubers from African elite cultivars by blocking the accumulation of cyanogenic glucosides, enhancing the protein content, and increasing the pro-vitamin A content. Future goals involve engineering resistance to important pests and diseases in the very same lines.

Climate change has spurred a worldwide demand for drought-tolerant plants, such as cassava. Likewise, as Western industrialized countries move towards a bio-based society less dependent on fossil fuels, starchy plants that can produce very high yields under optimal growth conditions become key targets for research. As part of these efforts, the cassava genome is now being sequenced in the US. When the genome sequence is available research on cassava will be that easier and may be the first step in developing the crop as an efficient environmentally benign “green factory” for producing valuable chemicals and pharmaceuticals.

The cassava group at the University of Copenhagen is headed by Professor Birger Lindberg Møller and principal investigator Associate Professor Kirsten Jørgensen, together with Assistant Professor Rubini Kannangara, Technicians Charlotte Sørensen, Evy Olsen, and Susanne Bidstrup, and gardener Steen Malmmose.

The power of small

People tend to overlook the “small” and “insignificant”, focusing more on the “big” and “obvious”. In economic development, micro-businesses often receive less attention and access to growth-enhancing support facilities. Their contribution is also often undervalued.

Until recently in Nigeria, when people discussed economic development, they mainly talked about the oil and natural gas industries. These industries account for nearly 100% of earnings and more than 80% of government revenues1 and they receive all the inputs and attention. Small-scale agriculture and agriculture-based enterprises are hardly ever talked about, as if they contribute very little to economic development. And yet agriculture still provides more than 60% of employment.

During the last 3-5 years, cassava has joined oil in the headlines. Because it is a highly important element in the Nigerian diet, growing cassava is embedded in the daily routine in many rural areas and city suburbs. For many years, it was considered a woman’s subsistence crop. Things changed when the Presidential Initiative on Cassava was introduced early in 2002 by then President, Chief Olusegun Obasanjo. A directive of the Federal government followed instructing bakers to include 10% cassava flour in the production of bread and confectionery. Two years later, the directive urged flour millers to buy high quality cassava flour from local processors. This has encouraged both farmers and processors to produce large volumes of this good quality cassava flour.

In line with the Cassava Presidential Initiative, IITA implemented the Integrated Cassava Project (ICP). Through its two subprograms, the Preemptive Management of Cassava Mosaic Disease Project (CMDP) and the Cassava Enterprise Development Project (CEDP), ICP aims to reduce the impact of cassava mosaic disease (CMD) and increase productivity in 11 states in the south-south and southeast of Nigeria. The project benefits farmers, many of them smallholders, and small and medium cassava-processing enterprises (SMEs).

Through strong partnerships with the government, private sector, and farmers, the project deployed and tested 40 new cassava varieties to counter the threat of CMD and increase yield. Usually it takes 6-8 years to release a new variety in Nigeria, but in agreement with various partners, ICP adopted a participatory approach that led to the official release of 10 new varieties in just 2 years.

This had dramatic results. A disease monitoring field survey in 2006 found no severe forms of CMD, and 10-30% of fields were completely free. A similar survey in 2007 showed that disease incidence in fields with mixed virus infections on the same plants had dropped by 20%. The two variants of CMD can recombine to form the virulent Ugandan mosaic virus.2

The Project continues to distribute planting materials of these varieties. Recorded yields were impressive, averaging 25.6 t/ha, a significant increase over the 12 t/ha from traditional varieties. Some beneficiaries got even higher yields at 30-50 t/ha.

CEDP was implemented in 2004 to increase economic opportunities through sustainable and competitive cassava production, processing, marketing, and enterprise development. It links farmers to processors and facilitates processors’ access to basic technologies and markets. It provides training on production and business development services, such as planning, record keeping, pricing, developing market linkages, sanitation and hygiene, and machine maintenance.

On the production side, nearly 250,000 farmers have benefited so far. They were trained on proper farm management and rapid multiplication techniques. Farmers succeeded in rapidly multiplying the planting materials and are gaining from increased income from greater production and sales and by selling cassava stems as well. In support and to provide a means of employment and income, a group of young people has been trained on proper weed control techniques to provide service whenever needed.

Other beneficiaries are the processors, including the mobile graters, microprocessing centers (MPCs), and the SMEs, which serve as market outlets to farmers.

Cassava is bulky and heavy. With the mobile grating service, women were able to save time and labor for other productive activities. The project created employment and income for the beneficiaries, mostly youths.

The MPCs, which are equipped with more facilities, can produce 1 t/day with basic equipment such as a grater, press, sieve (manual or motorized), and fryers. Owned mostly by cooperatives and women’s associations, the MPCs produce value-added cassava products for sale, and provide service—grating, pressing, or frying—to the public.

SMEs produce value-added cassava products. They have processing equipment similar to that in the MPCs but usually of higher capacity or more sophistication, such as flash and rotary driers. CEDP provided only a few of the machines for the MPCs and SMEs. The beneficiaries acquired most of them from more than 20 machine fabricators who had been trained by IITA and are now manufacturing machines of better quality and efficiency.

In collaboration with partners, especially the Agricultural Development Program in each beneficiary-state, CEDP provided intensive training for MPCs and SMEs on producing improved and high-quality flour, odorless fufu, garri, starch, chips, and their uses for industry as well as human consumption. A recipe book was also published.

Overall, the project introduced 22 technologies for beneficiaries, generating a total gross income of US$50 million, and creating 6,000 jobs. They gained knowledge and skills in farming and business development. The cooperatives and women’s associations became stronger.

Through continuous collaboration with IITA, some of the SMEs have scaled up their farm production. Now Nigeria has factories producing glucose syrup, ethanol, adhesives, and starch, all using cassava raw material and assisted by ICP.

These enterprises may be small, but with assistance and opportunity, the small could become powerful instruments of economic development.

1 Economy of Nigeria. 2008.
2 IITA Integrated Cassava Project. 2007.