Sustainable production and distribution of clean banana

Bi Irie Vroh, b.vroh@cgiar.org

Banana (Musa spp.) including the plantain type are among Africa’s most important staple food and cash crops. Nearly 30 million t of banana are produced yearly in Africa, mostly by smallholders and consumed locally.

The major edible types are parthenocarpic (produces fruit without fertilization) and seedless. They are propagated traditionally by planting corms and suckers (daughter plants that grow from the rhizomes at the base of mother plants).

However, propagation material derived from the infected mother stocks results in perpetuation of diseases (e.g., viruses such as banana bunchy top, banana streak) and pests (e.g., nematodes and weevils) leading to low yields and poor quality fruits.
Due to the unavailability of disease- and pest-free or clean planting materials, farmers in sub-Saharan Africa traditionally plant suckers derived from their own plantations, most of which are affected with pests and diseases.

IITA has been using three approaches to generate clean planting material of farmer-favored banana cultivars:

Boiling water treatment of suckers: Suckers are submerged in boiling water for 30 seconds to kill nematodes and weevils. This method is efficient and easy for farmers, but it has low output and is laborious.

IITA’s Emmanuel Njukwe, Paula Bramel, and Bi Irie Vroh visit the Fritz Jakob Foundation. Source: B. Vroh, IITA.
IITA’s Emmanuel Njukwe, Paula Bramel, and Bi Irie Vroh visit the Fritz Jakob Foundation. Source: B. Vroh, IITA.

Macropropagation using the PIF technique: Through the technique known as PIF (plantes Issues de Fragments de tige) tens of good quality plantlets are produced within two months at relatively low costs. In this approach, the primary buds of entire suckers or fragments of corms are destroyed and axillary buds are exposed to high humidity to induce sprouts which are then harvested, hardened, and distributed.

This approach can be implemented in remote rural areas near farmers’ fields or by NGOs in direct contact with farmers for training and the distribution of good planting materials. This procedure is simple to replicate using locally made humidity chambers.

Micropropagation: Also known as in vitro production of tissue culture (TC) material this is the most efficient approach to the production of clean planting material in terms of throughput and germplasm exchanges across international borders. In vitro plantlets are micropropagated in the TC laboratory of IITA in Ibadan, Nigeria, and hardened first in the acclimatizing rooms, then in screenhouses before being distributed to farmers. Planting materials from preferred landraces and improved hybrids are propagated through TC, and hardened for use or maintained in a conservation cold room where each genotype is replicated several times from the initial meristem for future use.

IITA’s Delphine Amah holding racks of TC plants in a growth room. Source: B. Vroh, IITA.
IITA’s Delphine Amah holding racks of TC plants in a growth room. Source: B. Vroh, IITA.

Combining the TC pipeline with the macropropagation through PIF, IITA regularly distributes thousands of seedlings to NARS, NGOs, and farmers in West and Central Africa. Besides the preferred local varieties, the most distributed improved materials include the plantain hybrids PITA 14, PITA 21, and PITA 23 and the cooking banana hybrid BITA 3. These hybrids express a higher level of tolerance for black Sigatoka diseases compared with local varieties.

IITA trains farmers in applying boiling water treatment of suckers and macropropagation by PIF to produce clean planting material. However, IITA primarily uses micropropagation as the method of choice for conservation, propagation, and distribution of germplasm, and also to support its breeding programs. IITA also provides training programs on TC operations for NARS. For IITA’s projects in West Africa, clean planting materials are produced by TC or by PIF, hardened and raised in screenhouses, and then transferred to specific project sites.

Hardening of clean planting materials produced by TC and PIF methods. Source: B. Vroh, IITA.
Hardening of clean planting materials produced by TC and PIF methods. Source: B. Vroh, IITA.

In rural communities, IITA emphasizes training for farmers and rural entrepreneurs so they can produce clean planting materials in their own communities. These various efforts enhance the farmers’ access to clean planting materials and also encourage involvement of commercial operators in distribution of planting materials. The improvement of the capacity of NARS and the involvement of the private sector are needed to scale up the technologies for the sustainable production of clean planting materials of banana and plantain.

Developing clean seed systems for cassava

James Legg, j.legg@cgiar.org

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.

Clean yam tubers from vine cuttings

Hidehiko Kikuno, h.kikuno@cgiar.org

Production of yam seed tubers using vine cuttings and in vitro micropropagation is quick, cost-effective, and results in clean planting material. This new propagation system for yam developed by IITA uses vine cuttings grown on carbonized rice husks combined with in vitro micropropagation (tissue culture).

The traditional system uses tubers as seeds, is inefficient and costly. High production costs are attributed to the use of seed yam tubers, which account for about 30% of the total yield and as much as 63% of the total variable cost incurred per season of cultivation. The multiplication rate in the field using the traditional system is also very low (1:5 to 1:10) compared, for instance, with some cereals (1:300). Low quality seed yam containing pests (nematodes) and pathogens (viruses) also result in a poor yield of ware yam tubers.

Clean seed tuber production system using vine propagation in combination with tissue culture techniques. Source: H. Kikuno, IITA.
Clean seed tuber production system using vine propagation in combination with tissue culture techniques. Source: H. Kikuno, IITA.

The use of vine cuttings as a planting material gives a higher multiplication rate that is about 20−50 times more than the traditional system. It also significantly lowers the risk of nematode infestation and promotes faster multiplication and better and more uniform crop quality. Although viruses are difficult to eliminate, planting materials (seedlings or tubers) produced by this approach are relatively clean compared with those from other propagation methods used in the open field.

An experiment conducted from 2009 to 2010 using seed tubers produced by vine propagation and planted at 25 cm × 1 m spacing resulted in the production of tubers both large (200−400 g) and small (<10−30 g). Large tubers are suitable for use as seed yam for planting in the field, whereas small tubers are resown to obtain appropriately sized seed yam (about 200−400 g) (Table 1).

Tubers from vine cuttings. Photo by. H. Kikuno, IITA
Tubers from vine cuttings. Photo by. H. Kikuno, IITA

Attempts are also being made to standardize the procedure for the direct use of vine cuttings as planting material using cv. TDr 95/18544. The success of this approach could change the way in which yam is propagated in the future and eliminate the dependence on seed yam for planting needs. It would also boost the availability of yam by ~30% (Table 1).

Another trial conducted to understand the appropriate time to excise vine cuttings established from tissue culture materials revealed that the best time for vine cutting is before the rapid tuberization stage. Vine cuttings taken after tuberization were poorly established (see figure below; Kikuno et al. 2010).

Correlation between rooting of vine cuttings and dry weight of tubers formed on mother plants. Time course of rooting of wild vine cuttings and growth of tubers of mother plants on yam (D. alata cv. 95/00361). Bars in each figure indicate % of vine cuttings with rooting. Source: H. Kikuno.
Correlation between rooting of vine cuttings and dry weight of tubers formed on mother plants. Time course of rooting of wild vine cuttings and growth of tubers of mother plants on yam (D. alata cv. 95/00361). Bars in each figure indicate % of vine cuttings with rooting. Source: H. Kikuno.

This new technology offers a rapid solution for a high-output production of seed yam or yam planting material. At the same time, it addresses the need for large numbers and the quick distribution of improved varieties to farmers. This knowledge would be useful for NARES, CSOs, and farmers involved in producing and distributing seed yam, and in maintaining and multiplying breeder and foundation seeds. The technologies can also be used as a research tool by scientists.

The project was funded by the Japanese Government (Ministry of Foreign Affairs), Sasakawa Africa Association, Tokyo University of Agriculture, and International Cooperation Center for Agricultural Education at Nagoya University in Japan under the Ministry of Agriculture, Forestry and Fisheries funded the project. Partners include the Tokyo University of Agriculture; National Root Crops Research Institute at Umudike, Nigeria; Crop Research Institute, Ghana; and Institute of Agricultural Research for Development, Cameroon.

Reference
Kikuno H, Matsumoto R, Shiwachi H, Toyohara H, and Asiedu R. 2007. Comparative effects of explants sources and age of plant on rooting, shooting and tuber formation of vine cuttings from yams (Dioscorea spp.). Japanese Journal of Tropical Agriculture 51, Extra issue 2.

Joining hands to fight the legume pod borer

Manuele Tamò, m.tamo@cgiar.org

Maruca vitrata larva affected by the entomopathogenic virus MaviMNPV. Photo by S. Srinivasan, AVRDC.
Maruca vitrata larva affected by the entomopathogenic virus MaviMNPV. Photo by S. Srinivasan, AVRDC.

A new collaborative project has been launched to develop novel approaches against an old problem affecting cultivated legumes—the pod borer Maruca vitrata.

This is one of the major pests of cowpea in West Africa, where, if left uncontrolled, it can lead to 80% yield losses.

Under this new project, funded by the German Federal Ministry for Economic Cooperation (BMZ), IITA and partners, the World Vegetable Center (AVRDC), and the International Center for Insect Physiology and Ecology (icipe), will test a range of new natural enemies against the legume pod borer. In close collaboration with national agricultural research systems (NARS) and scientists and colleagues in the Plant Protection and Quarantine Services, the project will choose the most promising natural enemies adapted to West and East African conditions.

One of the major outcomes of this project will be to quantify the impact of selected biocontrol agents on the population ecology of the pod borer and on cowpea yield in the field. At the same time, detailed molecular analysis of pod borer populations from different parts of the tropics, Africa, South America, and Asia, in collaboration with the BMZ project and a Dry Grain Pulses Collaborative Research Support Program (DGP-CRSP) project with the University of Illinois, will permit the identification of scoreable polymorphisms for determining the genetic similarity and differences between pod borer populations at distant locations. This will enable project staff to answer questions in relation to differential responses to synthetic pheromones, the diversity of biocontrol agents, and the development of an insect resistance management plan in preparation for the deployment of Bacillus thuringiensis (bt) cowpea in the region.

Experimental release of Apanteles taragamae using caged Sesbania cannabina. Photo by M. Tamo, IITA.
Experimental release of Apanteles taragamae using caged Sesbania cannabina. Photo by M. Tamo, IITA.

Prior to this new project, AVRDC and IITA have already collaborated, both formally and informally, on research on pod borer control. Biodiversity studies carried out at AVRDC in Taiwan had identified the exotic parasitoid Apanteles taragamae as the most promising candidate. This was subsequently introduced into the laboratories of IITA Bénin station. After a series of pre-release tests, experimental inoculative releases of A. taragamae were carried out between February and June 2007 in Bénin, Ghana, and Nigeria. The sites were patches of wild vegetation including plants known to host the pod borer, such as the legume trees Lonchocarpus sericeus, Pterocarpus santalinoides, and the shrubs Lonchocarpus cyanescens and Tephrosia spp.

As early as 6 months after the first releases IITA started a series of surveys to monitor the establishment of the parasitoid in the neighborhood of the releases. The monitoring continued until 2009, during which time we were not able to recover the parasitoid. However, we found indirect evidence of establishment in the environment (see below). We ruled out the theory that interspecific competition with indigenous parasitoids exploiting M. vitrata larvae of the same age and on the same host plant was the cause for this lack of evidence. We had conducted, just before the releases, quite elaborate competition studies which did not reveal any problems. Also, in its area of origin in Taiwan, A. taragamae coexists with similar parasitoid species found in Bénin, e.g., Phanerotoma sp. and Dolichogenidaea sp.

In Taiwan, however, A. taragamae is found prevalently on the cover crop Sesbania cannabina. This has been difficult to grow in West Africa because of foliage beetles (particularly Mesoplatys sp.) that completely defoliate the plant. We also intensified our studies on African indigenous species of Sesbania which suffer less beetle damage. So far, there have been no signs of direct establishment, although screenhouse experiments have confirmed the suitability of Sesbania spp. both as a feeding substrate for the pod borers and as a host for foraging parasitoids.

More recently, with funds from DGP-CRSP, we have developed a new release system using caged S. cannabina, infested artificially with eggs of M. vitrata, and subsequently inoculated with adult A. taragamae. Preliminary results indicate that such a cage can produce up to 300 cocoons of the parasitoid. At this stage, the cage can be removed and the parasitoids can emerge from the cocoons and disperse in the surrounding natural habitat. This deployment system is currently under testing in Bénin.

Adult female of Maruca vitrata. Photo by G. Goergen, IITA.
Adult female of Maruca vitrata. Photo by G. Goergen, IITA.

Another important beneficial organism which was identified by AVRDC in Taiwan is the Maruca vitrata Multi-Nucleopolyhedrosis Virus (MaviMNPV). This was imported to IITA-Bénin for further assessment. Again, after a series of laboratory tests which confirmed the results obtained in Taiwan and ascertained the specificity of MaviMNPV to the target host, IITA proceeded to test the virus in seminatural conditions. For this, we used field cages with artificial infestations of M. vitrata larvae. These experiments were also replicated in the screenhouse in Kano, Nigeria. Both tests indicated a very high mortality of pod borer larvae (>95%) using standard concentrations comparable to those found in commercial formulations of entomopathogenic viruses (e.g., against the cotton bollworm Helicoverpa armigera).

In Bénin, we did not carry out any open field experiments, so we were puzzled to discover a few pod borer larvae collected in the Mono region, close to release sites of the parasitoids, with apparent signs of the virus (Note: MaviMNPV had never been found in Bénin nor anywhere else in West Africa prior to the introduction in 2007, as confirmed by surveys of Dr A. Cherry in collaboration with the Natural Resources Institute).

Based on this discovery, and also aided by literature support, we attempted to verify the hypothesis that the parasitoid A. taragamae could have transmitted the virus MaviMNPV to pod borer larvae. We used three different infection methods (ovipositor only, whole body without ovipositor, and indirectly through artificial diet) to test the hypothesis. Results confirmed that the parasitoid was able to transmit the virus to the larvae through any of the infection methods. This discovery is quite significant: the parasitoid may be able to spread the virus in the environment without any further intervention.

This is also indirect evidence that A. taragamae is present in the environment, maybe at low levels, that cannot be detected by current sampling methods, or on secondary host plants for M. vitrata whose identity is still unknown. Further studies indicated that A. taragamae females can pass on the virus up to the third generation.

At present, we are looking for low-cost and efficient ways of producing the parasitoid and the virus so that the technology can be implemented by NARS colleagues and cottage industries at the community level, with financial support from DGP-CRSP. Also, training and demonstration videos of the major cowpea pests, their natural enemies, and detailed rearing methodologies are being prepared.

Improved cowpea varieties for Nigeria’s savannas

Nigeria has released two new cowpea varieties to raise production and improve farmers’ incomes.

Harvesting cowpea. Photo by IITA
Harvesting cowpea. Photo by IITA

The varieties—IT89KD-288 and IT89KD-391—were developed by scientists working at IITA, Ibadan, in collaboration with the Institute for Agricultural Research of the Ahmadu Bello University, Zaria; University of Maiduguri, Borno; and the Agricultural Development Programs of Borno, Kaduna, Kano, and Katsina States.

Both varieties have proven to be superior over the current improved lines being cultivated. They could be used to overcome the challenges faced by cowpea farmers in the country.

For instance, IT89KD-288 (now SAMPEA-11) is a dual-purpose cowpea variety with large white seeds and a rough seed coat. It has combined resistance to major diseases including septoria leaf spot, scab, and bacterial blight, as well as to nematodes, and tolerance for Nigeria’s strain of Striga gesnerioides (a parasitic weed that severely lowers yield).

“It also has a yield advantage of at least 80% over the local varieties,” said Alpha Kamara, IITA Agronomist, who is leading efforts to rapidly disseminate the varieties to farmers.

The nematode-resistant variety is an equally good candidate for sowing with cereals or as a relay crop with maize in the moist and dry savanna zones, and for high grain production in the dry season.

Scientists recommend that the variety be planted in mid-July in the Sudan savanna, early to mid-August in the northern Guinea savanna, and by the end of August in the southern Guinea savanna. However, if there is certainty of rains up till the end of October, IT89KD-288 can be planted in September.

Cowpea farmers in Kano, Nigeria. Photo by IITA.
Cowpea farmers in Kano, Nigeria. Photo by IITA.

IT89KD-391 (now SAMPEA-12) is also a dual-purpose cowpea variety but it has medium-to-large brown seeds with a rough seed coat. These are preferred seed characteristics for commercial production in northeast Nigeria.

“IT89KD-391 is a welcome improvement over SAMPEA 7, Ife brown, IT90K-76, and IT90K-82-2 which are the main improved brown-seeded varieties available. It has been tested extensively in this area and is well accepted by the farmers,” said Hakeem Ajeigbe, IITA Extension/Dissemination Specialist.

“The variety performs well as a sole crop and an intercrop. It could also be planted as a relay crop with maize in the Guinea savannas,” he added.
Several on-station and on-farm trials have shown that IT89KD-391 (SAMPEA 12) produces double the yields of local cultivars.

In 2008, Nigeria released a Striga-resistant improved cowpea variety (IT97K-499-35).

“The demand for these improved varieties is high because of their superior yields and their acceptability by consumers,” Kamara said.

Cassava: improving sustainability of farming systems

Anneke Fermont, a.fermont@cgiar.org

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.

Participatory strategies of conserving yam biodiversity in Bénin

A. Dansi (adansi2001@gmail.com), C. Lusty (charlotte.lusty@croptrust.org), R. Asiedu (r.asiedu@cgiar.org), R. Hall, and R. Vodouhè (r.vodouhe@cgiar.org)

Yam (Dioscorea spp.) is an important tuber crop in Bénin. Its production is intensive in Collines (Center), Donga and Borgou (North), but marginal in Atakora (Northwest), Plateau (Southeast), and in Alibori (far north). Four species are cultivated (D. alata, D. cayenensis-rotundata complex, D. dumetorum, and D. bulbifera). Among these, the native African D. cayenensis-rotundata complex remains the most important, preferred, and widely cultivated.

Yam tuber seeds of different accessions ready for transport to IITA genebank for ex situ conservation. Photo from Alexandre Dansi, IRDCAM.
Yam tuber seeds of different accessions ready for transport to IITA genebank for ex situ conservation. Photo from Alexandre Dansi, IRDCAM.

Yam production in Bénin is seriously hampered by numerous constraints including pest and disease pressure, poor soil, and changing climate. Strategic use of existing genetic diversity is thus an appropriate option for addressing these constraints in an affordable and sustainable way. For this diversity to be well studied, conserved, and used, the International Foundation for Science (IFS), Gatsby Charitable Foundation (UK), IITA, Bioversity International, and more recently the Global Crop Diversity Trust (GCDT) sponsored several research projects in Bénin between 1997 and 2009. Within the framework of these projects, different yam germplasm collection surveys have been conducted that led to a unique collection of 1,017 accessions conserved in the field by Crop, Aromatic and Medicinal Plant Biodiversity Research and Development Institute (IRDCAM) in northern Bénin.

The landraces collected were fully documented (origin, agronomic traits, and technological characteristics) and a database was constructed. With the help of farmers, the collected landraces have been fully characterized based on plant morphology and classified into 210 morphotypes. The equivalence of the diverse vernacular names that cause confusion among users has been clearly established. The geographical distribution of the morphotypes, together with genetic diversity analysis, led to the identification of four different zones of diversity. These are Zone 1: Atakora (far Northwest); Zone 2: Bariba cultural area (Northeast); Zone 3: Donga (Northwest); and Zone 4: South-Center.

Yam germplasm collection points. Courtesy of GIS Lab, IITA.
Yam germplasm collection points. Courtesy of GIS Lab, IITA.

Analysis at the community level within each of these four zones revealed the high yam diversity in Bénin in Zone 2 (20–82 varieties per village; 40 on average) and in Zone 3 (13–48 varieties per village; 24 on average). Zone 1 (8–27 varieties per village; 17 on average) and Zone 4 (6–51 varieties per village; 20 on average) had less diversity. Early maturing (double-harvested) varieties dominate Zones 1 and 4, while Zone 3 is dominated by late-maturing (single-harvested) varieties. Both late- and early maturing landraces appeared in almost equal proportions across villages in Zone 2.

Within each of the four diversity zones and at community level, several varieties are disappearing or being abandoned. High rates of genetic erosion (32–48% on average) were recorded almost everywhere. This highlights the necessity and urgency of developing strategies to conserve the existing diversity both in situ and ex situ for use by present and future generations. With the financial support of GCDT, Bénin yam germplasm is already fully regenerated and safely duplicated in IITA’s Genetic Resources Center at Ibadan (Nigeria) where it will be conserved both in vitro and in a field bank.

The causes of the ongoing genetic erosion are diverse (technological, biotic, abiotic, and cultural) and vary in relative importance according to production zones. In the far Northwest (Zone 1), for example, environmental factors, particularly poor adaptation to climate change and susceptibility to poor soils, are the most important. In the Northeast (Zone 2) susceptibility to pests and diseases and cultural beliefs are the principal reasons.

To compensate for the loss in diversity and cope with the environmental (biotic and abiotic) constraints, farmers use different strategies to exploit the existing diversity. In the dry zone of Atakora where climate change is more perceptible, farmers adopt new varieties to adapt production to actual local conditions that are characterized by increasing frequency of drought. They also alter the timing of planting and other agronomic practices. In central Bénin, farmers increasingly neglect D. cayenensis rotundata varieties in favor of those of D. alata since these are better adapted to current agroecological conditions (poor soil, pest and disease pressure, low rainfall, etc.).

To assist farmers with this option for using the genetic diversity, a program for intensive variety exchanges between villages and producers in different diversity zones was launched in 2009 within the framework of the GCDT project. Of 20 to 30 participating villages in each zone, 15 villages have already received new varieties (40 to 50 per village). This year, 15 other villages will also benefit from this program.

Alexandre Dansi (right) and some farmers from Tchakalakou (North Bénin) in a discussion during the participatory yam characterization and classification exercise. Photo from Alexandre Dansi, IRDCAM.
Alexandre Dansi (right) and some farmers from Tchakalakou (North Bénin) in a discussion during the participatory yam characterization and classification exercise. Photo from Alexandre Dansi, IRDCAM.

The exchanges have been conducted, taking into account the preference criteria determined for each zone. This exchange of varieties is a strategic way of conserving diversity on-farm through utilization. It has a multidimensional importance that includes strengthening yam production, food security, poverty alleviation; improvement of household income generation; strengthening diversity, conservation, and use; and improvement of sociocultural conditions of rural women. The results will rapidly become more evident in Zone 1.

In the northern part of this zone negatively affected by climate change, only one to two varieties out of eight to ten are tolerant of drought. The weather is suitable for the production of dry yam chips, which are in high demand and more expensive than fresh yam, but the late-maturing varieties used for this purpose were almost absent. In the south of the zone (Toucountouna and Natitingou region) dominated by lowlands, flooding is a challenge and only a few varieties were reported to be tolerant of high soil moisture.

We believe that by using, through exchanges, a large number of the Bénin yam varieties available, farmers in these regions will have a chance to find at least 50 that will be suitable for their local conditions. A strong network of yam producers in Bénin is actually being organized by IRDCAM to sustain the effort. The farmers highly appreciate the effort.

Cultivated yam are all domesticated from wild relatives co-evolving with the cultivated forms via gene flows. Because these species are sources of useful genes, participatory strategies have also been developed to preserve their diversity in situ while encouraging the domestication process developed by farmers.

Safeguarding against locust invasion

Nomadacris septemfasciata hopper band
Nomadacris septemfasciata hopper band. Photo from Wikimedia Commons

Fourteen years after the introduction of the fungal biopesticide—Green Muscle®—developed by IITA’s scientists with their partners, the product is gaining more prominence as a control option against invasive locusts that threaten African farmlands.

Recently, the biopesticide, which had been picked up by a South African firm for commercialization, averted the devastation of farmlands from an invasion of red locusts in Tanzania.

The rapid intervention by the Food and Agriculture Organization (FAO) using the biopesticide drastically reduced locust infestations in Tanzania and prevented a full-blown invasion that could have affected the food crops of around 15 million people in the region.

Ignace Godonou, entomologist based in IITA-Bénin, was part of the team that developed the biopesticide more than a decade ago. He said that, if left uncontrolled, a full-blown invasion would have caused a major setback to food security in the region.

“We are happy that Green Muscle® has proved effective in controlling locusts and is now widely used.”

Green Muscle® is a fungal biopesticide that was developed in response to a locust plague in the 1980s. It is effective against most locust and grasshopper species; it is safe, does not affect other species, and can be sprayed in the same way as chemical pesticides. A fungus, Metarhizium anisopliae, which is common in the tropics and subtropics, is used to kill the pests.

Top: Healthy hopper; Bottom: Hopper infested with Metarhizium
Top: Healthy hopper; Bottom: Hopper infested with Metarhizium. Photo by IITA

If not restrained, large swarms of red locusts will fly over vast areas of farmland, traveling daily more than 20 or 30 km and feeding on cereals, sugarcane, citrus and other fruit trees, cotton, legumes, and vegetables cultivated by poor farmers. A red locust adult consumes roughly its own weight in fresh food, about 2 g, in 24 hours. A very small part of an average swarm (about 1 t of locusts) eats the same amount of food in one day as around 2,500 people.

The biopesticide was developed by an IITA technical team under the LUBILOSA project (LUtte BIologique contre les LOcustes et les SAuteriaux – Biological Control of Locusts and Grasshoppers). It has proved effective in controlling locusts in the Sahelian region, including the Republic of Niger and Mauritania.

Godonou said that initial field trials of the product were conducted in the Republic of Bénin under the close watch of IITA scientists, based in Cotonou. The subsequent large-scale field trials were held in Niger and Mauritania.

“Mass production of the fungus for small- to large-scale field trials also started at IITA-Bénin,” he added.

“Moreover, it can persist in the ground for several weeks or for up to a year after spraying, continuing to attack and kill healthy locusts and grasshoppers. The fungus is very safe and has a narrow range of hosts,” said Godonou.

This environment-friendly alternative to synthetic chemical pesticides weakens and kills the locusts in 10 to 14 days, continuing to attack and kill the grasshoppers. It remains effective under prolonged dry conditions and is therefore more effective as a control agent. The fungal spores are suspended in an oil solution, giving the product its green color.

Apart from IITA, other leading institutions in the LUBILOSA project were the Commonwealth Agricultural Bureau International in the UK, and the Département de Formation en Protection des Végétaux in Niger, with many partners drawn from donors, several research institutes, national agricultural research and extension systems, nongovernmental organizations, FAO, private sector companies, and farmers.

Recipe for African farmlands

Damage by cassava green mite
Damage by cassava green mite. Photo by IITA

A natural enemy, capable of tackling the green mite menace, has been helping millions of Africans whose livelihoods depend on cassava.

The natural enemy, Typhlodromalus aripo, has proven to be an ideal candidate in controlling the cassava green mite (Mononychellus tanajoa) after 7 years of studies, says Dr Alexis Onzo, IITA entomologist based in Cotonou.

Back in the 1970s when the pest entered Africa, cassava green mite wreaked havoc on African cassava farms, depleting yields, in some cases, up to 80%.

Onzo says the neotropical spider mite attacks cassava—a major crop in Africa—by damaging the photosynthetically active leaf surface area of the plant.

The good news, however, is that the biocontrol option which saw the introduction of T. aripo in Africa has substantially reduced the population of green mites, as evident in studies carried out by scientists in southwestern Bénin and in many other countries in the African cassava belt. The results indicate that the introduction of T. aripo has helped in ensuring farms with healthier cassava plantations in Africa.

The predatory mite, T. aripo, was introduced by IITA and partners from Brazil, South America for the control of the cassava green mite. It resides primarily in the apices of the cassava plant, feeding on and reducing the populations of green mites not only in the apices but also in the upper part of cassava foliage.

Alexis Onzo inspects cassava leaves for pests
Alexis Onzo inspects cassava leaves for pests. Photo by IITA

Onzo says T. aripo was released in Africa by IITA and partners in the 1990s to contain the devastation caused by green mites. Since then the natural enemy has, on its own, been spreading to different parts of the continent, playing its role as a natural control agent against that cassava pest.

Unlike chemical control which wipes out the pests and other benevolent species, the biocontrol option reduces the population of the pest to a level that makes the pest’s impact on the crop economically insignificant. Besides, the pollution associated with chemical control is also avoided.

Onzo described the continuing success of green mite control in Africa as a welcome development and a victory for resource-poor farmers who will have the opportunity of cultivating healthier cassava farms.

With the prevention of the devastation by green mites and other pests, cassava has now become a cash crop in Africa, generating wealth and improving the food security of many Africans.

“Today we see cassava serving as a raw material in the flour, ethanol, and glucose industries. Even the governments are benefiting from these benefits,” he says.

As cassava green mite becomes less of a problem, Onzo says he intends to take up the fight against mites that are ravaging and depleting the production of coconuts and vegetables in Africa.

Biocontrol: saving the environment, saving farmers’ incomes

Water hyacinth grows fast and can clog water bodies
Water hyacinth grows fast and can clog water bodies. Photo by IITA

Biological control of water hyacinth is not only restoring the balance of nature in Africa but also putting savings in the pockets of resource-poor farmers whose livelihoods depend on fishing, thanks to IITA.

Using natural enemies, scientists have been able to control the purple-flowered water weed in southern Bénin, for instance, showing that annual incomes in that region increased by US$30.5 million.

The result of the studies, which was published in the Journal of Agriculture, Ecosystems & Environment, estimated the total cost of the biocontrol program at $2.09 million.

“Assuming that the benefits are to stay constant over the next 20 years—a most conservative assumption—the accumulated present value would be $260 million, yielding a respectable benefit-cost ratio of 124:1,” say Drs Hugo de Groote and Peter Neuenschwander.

Water bodies, such as lakes, rivers, and dams are important for agriculture and as water sources for domestic needs.

However, floating aquatic weed species mostly originating from South America, such as water hyacinth (Eichhorniae crassipes), water lettuce (Pistia stratiotes), giant salvinia (Salvinia molesta), and the red water fern (Azolla filiculoides) were deliberately or accidentally introduced from their native home into these water bodies as ornamental plants or for use in the aquarium trade. Because of their rapid reproduction by vegetative means and through seeds, these plants have attained a pest status.

Obinna Ajuono explains how water hyacinth invasion was brought under control using a weevil
Obinna Ajuono explains how water hyacinth invasion was brought under control using a weevil. Photo by IITA

Obinna Ajuonu, IITA entomologist, says the damage caused by water hyacinth, for instance, on the fishing community alone was devastating.

“It accumulates a large biomass that enables the plants to block waterways,” he explains, “thus impeding fishing and transport by boat or canoe, leading to increased transport costs and loss of revenue. They can also increase the incidence of diseases, such as bilharzia, and provide refuge for reptiles, such as snakes.”

A survey by IITA in southern Republic of Bénin in 1999 revealed that at the peak of the infestation, water hyacinth had reduced the yearly income of a community of about 200,000 people by approximately $84 million. Men lost revenue mostly in fishing, while women experienced loss of income in trade, primarily in food crops and fish.

The intervention by IITA and partners through the release of three natural enemies, two weevil species and one moth that feed exclusively on water hyacinth, however, brought succor to the West African region where the devastation was most extensive.

Neochetina eichhorniae, the weevil that brought water hyacinth under control
Neochetina eichhorniae, the weevil that brought water hyacinth under control

IITA implemented the first biological control of floating weed in West Africa (Bénin) way back in 1991 with the release of the weevil Neochetina eichhorniae that ate nothing but the water hyacinth at immature and adult stages. Biological control of water lettuce, giant salvinia, and the red water fern using their specific agents, followed thereafter.

From IITA-Bénin, a starter colony of biocontrol agents against aquatic weeds and expertise in implementing weed biological control were provided to other countries, such as Burkina Faso, Côte d’Ivoire, Ghana, Kenya, Nigeria, Republic of Congo, Senegal, Tanzania, Uganda, and Zimbabwe.

Other benefits brought by IITA’s intervention included an improvement in water quality and human health. Before the biological option was used, national governments in the subregion applied herbicides and mechanical/manual removal to control water hyacinth—options that were neither environmentally friendly nor cost-effective.

Ajuonu says an additional biological control agent for the water hyacinth is being planned. “The new ideal candidate is the mite Orthogalumna terebranti,” he explains. This has been discussed in several Economic Community of West African States (ECOWAS) meetings on aquatic weed control, where IITA was represented.

He explained that IITA provided many of the ECOWAS countries with starter colonies of agents and would continue to do so by importing the mite in 2009/2010 and maintaining a laboratory culture for supply to individual countries.