Ecofriendly bioherbicide approach for Striga control

Abuelgasim Elzein,, and Fen Beed

Root parasitic weeds of the genus Striga are a significant constraint to cereal and cowpea production in sub-Saharan Africa. They can cause total crop losses particularly during drought, in infertile soils and cereal monocropping. Striga causes annual losses of US$7 billion and affects incomes, food security, and nourishment of over 100 million people mostly in sub-Saharan Africa.

Each Striga plant can produce thousands of seeds, viable for over 10 years. Their intimate interaction with different host plants prevents the development of a silver bullet control technology that subsistence farmers can adopt. Hence, it is widely accepted that an integrated approach to Striga management is required for which biocontrol represents a crucial component.

Bioherbicide innovation
A bioherbicide is a plant pathogen used as a weed biocontrol agent (BCA), which is applied at sufficient rates to rapidly cause a disease epidemic that kills or severely suppresses the target weed. The use of biocontrol technology to manage Striga is a desirable control method as it is environmentally friendly, safe to farmers and crop consumers, specific to the target host, and has the potential to be economically viable. In addition, biological control also assists in the development of a balance of nature, the creation of more biodiversity, and sustaining of complex ecological interactions.

Since the early 1990s, a series of intensive disease surveys in many countries of sub-Saharan Africa has evaluated hundreds of microorganisms for their pathogenicity and virulence against Striga. Fusarium oxysporum Schlecht isolates have been the most promising. However, the discovery of a highly effective pathogen is only one step in the process of developing bioherbicides, for which the inoculum mass production, formulation, delivery, and storage ability must be optimized, and the mode of action, host specificity, and biosafety evaluated and fully understood.

The most widely studied and used fungal isolate that met all requirements for a potential bioherbicide for Striga is F. oxysporum Schlecht f. sp. strigae Elzein et Thines (isolates Foxy2 and PSM197). These are highly virulent, attack Striga in all growth stages—from seed to germination, from seedling to flowering shoot; protect the current crop yield; and prevent seed formation and dispersal.

F. oxysporum f. sp. strigae is highly host-specific to the genus Striga, and does not produce any known mycotoxic compounds. Thus, its use does not pose health risks to farmers, input suppliers, traders or consumers or threaten crops or the environment. Its unique DNA constitution differs from other forms of F. oxysporum deposited in GenBank, known to cause crop diseases. Indeed, this ensures its biosafety and greatly facilitates its wider application and use as a bioherbicide.

In addition techniques for massive production of inoculum of F. oxysporum f. sp. strigae was optimized based on simple and low-cost methods and using inexpensive agricultural by-products available in sub-Saharan Africa. The chlamydospores produced by this fungus have the advantage of being able to survive extreme environmental events while still remaining viable. This is an important feature required for a BCA suited to hot and dry climatic conditions of cereal production in sub-Saharan Africa, and to produce stable, durable, and pathogenic propagules.

Extensive research by the University of Hohenheim (UH, Germany), IITA (Benin), McGill University (Canada), and Institute for Agricultural Research – Ahmadu Bello University (Nigeria), has enhanced application of F. oxysporum f. sp. strigae, its formulation into bioherbicidal products, and its delivery for practical field application. The Striga bioherbicide contains the Striga host-specific F. oxysporum f. sp. strigae, applied in massive doses to create a high infection and disease level to kill or severely suppress Striga.

Promotion in West Africa
The bioherbicide is a component of the IITA-led project, Achieving sustainable Striga control for poor farmers in Africa, funded by the Bill & Melinda Gates Foundation to intensively promote technologies to combat Striga in sub-Saharan Africa. The project will validate the potential of the bioherbicide seed treatment technology across major Striga-infested agroecological zones and maize-based farming systems, while also confirming the biosafety and developing molecular detection tools. Here are the highlights of the results:

Technology validation: Several multilocation trials were conducted under natural and artificial Striga infestation across two agroecological zones in northern Nigeria to evaluate the efficacy of Striga bioherbicide (F. oxysporum f. sp. strigae). The inoculum produced by UH and SUET seed company was delivered as a film-coat on maize seeds (see below).The application of the bioherbicide technology in combination with Striga resistant maize reduced Striga emergence by 73% and 39%, compared to the susceptible and resistant controls, respectively, and prevented 81% and 58% of emerged Striga plants from reaching flowering and 56% and 42% of the maize plants from attack by Striga (see next page). The combination of bioherbicide with Striga susceptible variety significantly reduced Striga emergence by 53%, resulting in 42% reduction in number of flowering plants and in 21% increase in grain yield compared to the susceptible control.

In addition, disease symptoms were recorded on emerged Striga plants parasitizing maize plants coated by the bioherbicide. The reduction in Striga emergence across maize varieties indicates the effectiveness of the bioherbicide to attack seeds under the soil surface. The synergistic effect of the bioherbicide technology combined with the Striga resistant maize is expected to reduce the Striga seedbank and thus the impact of Striga on subsequent maize crops.

Biosafety: To further ensure the safety of Striga BCA and to demonstrate and increase awareness among farmers, regulatory authorities, and stakeholders, a wide host range study was carried out using 25 crops in collaboration with IAR-ABU and the Nigerian Plant Quarantine Service (NPQS)  under field and screenhouse conditions in Nigeria. Results revealed that none of the test plants showed any infection by the biocontrol agent both in the field and screenhouse, and no detrimental growth effects were measured or visual losses to plant health recorded in any of the inoculated crops tested, i.e., inoculation with the Striga BCA did not cause any delay in emergence, and a decrease in plant height, plant vigor, chlorophyll content per leaf, shoot fresh and dry weight. Hence, the Nigerian regulatory authorities (NPQS, NAFDAC) and other stakeholders were satisfied and confident that no disease was produced on plants other than Striga by the BCAs and that it is safe to use. In addition, a mycotoxin produced by Striga bioherbicide  F. oxysporum f. sp. strigae was analyzed and evaluated by our project partner, the University of Stellenbosch in South Africa. An evaluation of existing isolates of F. oxysporum f. sp. strigae does not produce well-known mycotoxins (e.g., Fumonisin and Moniliformin) that pose a threat to animal or human health. This finding further confirms the safety of this bioherbicide.

Molecular detection tools: Development of a monitoring tool specific to the Striga bioherbicide is important to certify inoculum quality, monitor the presence and persistence of the BCA in soils, and validate its environmental biosafety. UH is developing a monitoring tool.

The AFLP fingerprinting technique was successfully used in developing a primer pair capable of differentiating the F. oxysporum f. sp. strigae group from other Fusarium species. In addition, the monitoring tool has shown a high specificity for isolate Foxy2 and was used to monitor its spread and persistence in rhizobox experiments under different management practices using Kenyan soils. This promising result provides a proper baseline to further the existing primer set.

Bioherbicide + pesticide technology: The novel combination and integration of the bioherbicide technology plus imazapyr herbicide for Striga control with pesticides in a single-dose seed treatment to control fungal pests offers farmers with maize seed that is able to achieve its yield potential. The use of each technology (BCA or imazapyr) has been shown to be effective when applied independently using seed coating techniques, but have not been integrated.

The compatibility of Striga BCAs with different pesticides (herbicides and fungicides with insecticide components) was studied in vitro in the laboratory. Striga BCAs showed excellent compatibility with imazapyr (a herbicide seed coating used in combination with IR maize to control Striga), Metsulfuron Methyl (MSM) (a herbicide seed coating developed by DuPont to control Striga in sorghum), and glyphosate (an intensively used herbicide). A similar result was also achieved with the commonly used seed treatment fungicides at the recommended application doses.

Accordingly, doses and complementary seed coating protocols for the three compatible technologies (BCA, herbicide, and fungicides) have been developed and IR maize seeds were successfully coated with a single-dose seed treatment of BCA inoculums and imazapyr. The results showed that imazapyr did not interfere with the BCA during seed coating, with BCA growth and sporulation after coating, and with IR maize seed germination. Seeds of IR maize varieties can thus be coated with the herbicide and the BCA and then fungicide and delivered to farmers using the same input pathway. Screenhouse and field trials are being carried out to generate data on the combined efficacy of the applied technologies. The demonstrated compatibility of Striga BCA with the different pesticides that contain a wide range of active ingredients indicate that the combination and delivery of the Striga bioherbicide technology with a large number of pesticide products is possible. These findings are expected to provide a triple action seed coating package for direct control of Striga and fungal diseases of maize in sub-Saharan Africa.

Suitability to African farming systems
Our strategy for scaling-up the bioherbicide innovation is based on using technology appropriate to Africa to ensure that sustained production of the bioherbicide is feasible at a cost affordable to African small-scale farmers. The seed-coating treatment requires significantly less inoculums, establishes the BCA in the cereal rhizosphere, i.e., the infection site of Striga, and provides a simple, practical, cost-effective delivery system for adoption by input suppliers to subsistence farmers. Arabic gum as a coating material has been shown to increase the rate of mycelia development and enhance BCA sporulation. Its availability in sub-Saharan Africa at a low price is an additional economic advantage. A commercial seed coating process, developed and optimized at UH with SUET Seed Company in Germany, is being transferred and adapted at IITA, Ibadan, to be used as an experimental production unit for capacity building and as a model for eventual transfer of seed treatment technology to the private sector after validation.

One unique advantage of this bioherbicide is that the ability of Striga to become resistant to it is virtually unknown as a consequence of the suite of enzymes and secondary metabolites that the BCA produce to become pathogenic and virulent against the target (Striga). Hence after validation, delivering the bioherbicide technology in combination with resistant maize or with the herbicide imazapyr is expected to increase efficacy in controlling Striga. Bioherbicide and other compatible technologies have different modes and sites of action against Striga, and in a combination they will have a much greater chance of reducing the potential risk of development of resistance to a single technology (resistant varieties or herbicides) used separately and repeatedly.
The potential delivery of coated seeds of resistant maize with bioherbicide in one package to farmers using the same input pathway will reduce transaction and application costs and enhances the economic feasibility and adoptability of the technologies. Similarly, compatibility of BCA with imazapyr and fungicides allow seed coating of IR-maize with bioherbicide, imazapyr, and fungicides with a single-dose seed coating application.

Future plans
Currently, large-scale field testing is ongoing and is being implemented to further validate bioherbicidal efficacy across two agroecological zones where the common scenarios for maize infestation by Striga in northern Nigeria are represented. For understanding of farmers’ preferences and perceptions, socioeconomic analysis and cost-benefit analysis of bioherbicidal technology based on field data/surveys and interviews, current market information, and links with other Striga control strategies will be undertaken. After validation, dissemination and commercialization will be promoted through private sector partnerships and integrated with other control options such as resistant varieties, IR varieties combined with seed treatment with imazapayr, crop rotation with legumes, and soil fertility management practices, to achieve sustainable management of Striga.

IITA (Dr F. Beed, Dr A. Elzein & Dr A. Menkir), Institute for Agricultural Research – Ahmadu Bello University (Dr A. Zarafi), Nigeria; University of Hohenheim (Prof G. Cadisch, Dr F. Rasche & Prof J. Kroschel), Germany; The Real-IPM Company Ltd (Dr H. Wainwright), Kenya; University of Stellenbosch (Prof A. Vilioen), South Africa; and McGill University (Prof A. Watson), Canada.

Beed F.D., S.G. Hallet, J. Venne, and A. Watson. 2007. Biocontrol using Fusarium oxysporum; a Critical Component of Integrated Striga Management. Chapter 21 in Integrating New Technologies for Striga control: Towards ending the Witch-hunt (Ejeta, G. and J. Gressel, eds). World Scientific Publishing Co. Pte. Ltd. pp 283-301.

Ciotola, M., A. DiTommaso, and A. Watson. 2000. Chlamydospore production, inoculation methods and pathogenicity of Fusarium oxysporum M12-4A, a biocontrol for Striga hermonthica. Biocontrol Science and Technology 10: 129-145.

Ejeta, G. 2007. The Striga scourge in Africa: A growing pandemic In: Ejeta, G. and J. Gressel, eds. Integrating New Technology for Striga Control: Towards Ending the Witchhunt. World Scientific Publishing Co. Pte. Ltd., UK. pp. 3-16.

Elzein, A.E.M. 2003. Development of a granular mycoherbicidal formulation of Fusarium oxysporum “Foxy 2” for the biological control of Striga hermonthica. In: “Tropical Agriculture 12– Advances in Crop Research (2)” (J. Kroschel, ed.). Margraf Verlag, Weikersheim, Germany, 190 pp, ISBN 3-8236-1405-3.

Elzein, A., J. Kroschel, and V. Leth. 2006. Seed treatment technology: an attractive delivery system for controlling root parasitic weed Striga with mycoherbicide. Biocontrol Science and Technology, 16(1) 3-26.

Elzein, A., F. Beed, and J. Kroschel. 2012. Mycoherbicide: innovative approach to Striga management. SP-IPM Technical Innovations Brief, No. 16, March 2012.

Kroschel, J. and D. Müller-Stöver. 2004. Biological control of root parasitic weeds with plant pathogens. In: Inderjit, K. (ed.), Weed biology and management. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 423–438.

Kroschel, J., A. Hundt, A.A. Abbasher, J. Sauerborn. 1996. Pathogenicity of fungi collected in northern Ghana to Striga hermonthica. Weed Research 36 (6), 515–520.

Marley, P.S., S.M. Ahmed, J.A.Y. Shebayan, and S.T.O. Lagoke. 1999. Isolation of Fusarium oxysporum with potential for biocontrol of the witchweed Striga hermonthica in the Nigerian Savanna. Biocontrol Science and Technology 9: 159–163.

Venne J., F. Beed, A. Avocanh, and A. Watson. 2009. Integrating Fusarium oxysporum f. sp. strigae into cereal cropping systems in Africa. Pest Management Science 65: 572–580.

Saving maize from parasitic Striga in Kenya and Nigeria

Thousands of farmers in Kenya and Nigeria are successfully battling the invasion in their farms by Striga, a deadly parasitic weed. They are now enjoying higher yields in maize, the number one staple in Kenya and an important cash crop in Nigeria.

The key to managing this weed is to combine sustainable multiple-pronged technology options being advocated by the Integrated Striga Management in Africa (ISMA) project to sustainably eliminate the weed from their fields, says Dr Mel Oluoch, ISMA project manager.

Striga attacks and greatly reduces the production of staple foods and commercial crops such as maize, sorghum, millet, rice, sugarcane, and cowpea. The weed attaches itself to the roots of plants and removes water and nutrients and can cause losses of up to 100% in farmers’ crops. Furthermore, a single flower of the weed can produce up to 50,000 seeds that can lie dormant in the soil for up to 20 years.

The weed is the number one maize production constraint in Western Kenya, and Nigeria, infesting most farmers’ fields.

The management technologies range from simple cultural practices such as intercropping maize with legumes such as groundnuts; crop rotation of maize with soybean which stimulates Striga to germinate but which later dies in the absence of the maize host to latch onto; deploying a “push-pull’ technology that involves intercropping cereals with specific Striga-suppressing desmodium forage legume; using Striga resistant maize varieties; and using CIMMYT-developed maize varieties resistant to Imazapyr—a BASF herbicide (StrigAway®), which kills the Striga seed as it germinates and before it can cause any damage; and adopting Striga biocontrol technologies which uses a naturally occurring host-specific fungal pathogen that kills the Striga at all stages without affecting other crops.

Imazapyr-resistant maize varieties with natural resistance to Striga hermonthica have been developed. The best hybrids produce 19% to 333% more grain yields under Striga infestation, sustain 17% to 57% less Striga damage, and support 63% to 98% less emerged Striga plants compared with the commercial hybrid check. In addition, new Striga resistant hybrids and open-pollinated synthetic varieties (OPVs) that combine Striga resistance with good standability have been developed. The hybrids and OPVs produce 47% to 126% more grain yields under Striga infestation, sustain 17% to 60% less Striga damage, and support 45% to 90% less emerged Striga plants compared with the common farmers’ varieties and commercial hybrids.

ISMA ( is funded by the Bill & Melinda Gates Foundation and is being implemented with the International Center of Insect Physiology and Ecology, CIMMYT, African Agricultural Technology Foundation, BASF Crop Protection, and other national agricultural research and extension services and private sector players in Kenya and Nigeria.

Ensuring good quality commercial products

The ‘Institutionalization of quality assurance mechanism and dissemination of top quality commercial products to increase crop yields and improve food security of smallholder farmers in sub-Saharan Africa,’ or Commercial Products (COMPRO-II) project, was launched this year in Dar es Salaam, Tanzania.

Supported by the Bill & Melinda Gates Foundation, this project aims to institutionalize quality assurance mechanisms and facilitate the rapid dissemination of top quality commercial products to increase yields and improve the food security of smallholder farmers in the region.

This will be done by raising awareness among over two million smallholder farmers on effective and profitable commercial products by 2016 through public-private partnership.

1.transit technologies (e.g., Rhizobium inoculants for legumes, mycorrhizal inoculants for banana, and seed coating for maize) that enhance yields by 15–30% identified in COMPRO I into Ghana, Tanzania, and Uganda,
2.institutionalize regulatory and quality control processes,
3.disseminate effective products through public-private partnerships,
4.develop communication tools, and
5.strengthen human capacity.

Partners include the African Agricultural Technology Foundation (AATF), Alliance for a Green Revolution in Africa – Soil Health Program (AGRA), Farm Input Promotions (FIPS), the Tropical Soil Biology and Fertility Research Area of the International Centre for Tropical Agriculture (TSBF-CIAT), the Centre for Agricultural Bioscience International (CABI), and universities, national research organizations, extension organizations, and quality control entities in the different target countries.

Tanzania and partners tackle cassava disease

Tanzania’s Ministry of Agriculture, Food Security and Cooperatives (MAFC) and the Bill & Melinda Gates Foundation have launched three new projects to support efforts to develop cassava varieties with resistance to Cassava Mosaic Disease (CMD) and Cassava Brown Streak Disease (CBSD) and to establish more sustainable seed systems to provide smallholder farmers better access to such varieties.

The projects were launched during a cassava value chain event in Dar es Salaam that brought together representatives from the government, donor community, private sector and development partners.

Farmers in Tanzania and the region need access to planting materials of new improved varieties released in the country. Cassava is a very important crop not only for food security but it also has great potential as a cash crop through processing. The two diseases, especially CBSD, are a major problem and need to be urgently addressed.

The Cassava Varieties and Clean Seed to Combat CBSD and CMD (5CP) project will facilitate sharing of five of the best varieties from Tanzania, Kenya, Malawi, Mozambique, and Uganda for regional testing across the countries to speed up the development of varieties with dual resistance to the two diseases.

Valerie Bemo: Breakthroughs in African agric require collaboration

valerie-bemo-half-body Valerie Bemo (MD, MPH) is a native of Cameroon. She is a senior program officer in the Bill & Melinda Gates Foundation’s Global Development Special Initiatives. Before joining the Foundation, she held various roles at the International Rescue Committee, most recently serving as senior technical advisor for health in the Democratic Republic of Congo and West Africa. She also worked with various NGOs and had extensive involvement in Aceh, Indonesia, Côte d’Ivoire, Sierra Leone, Mauritania, Kenya, and Chad. Dr Bemo received her medical degree from the University of Côte d’Ivoire, her epidemiology diploma from the University of Paris, and her MPH from Madrid Autonome University.

Tell us about yourself.
Born in Cameroon and educated in Cameroon, Côte d’Ivoire, France, and Spain, I have spent the last 15 years working on community development at the district and national level in Africa, Asia, and Europe. My professional and personal time is devoted to various organizations that impact health and development on a global scale.

Please describe your work at the Foundation. What are your goals?
My role as a Senior Regional Adviser (SRA) for West Africa is to help the Foundation’s Agricultural Development team to establish and maintain relationships with key stakeholders that would lead to a greater impact of the Foundation’s investments in the region. Our initial countries are Mali, Ghana, Burkina Faso, and Nigeria. The work involves:
• Ground-truthing country context and developing country strategy
• Providing a voice from the region to the foundation’s Seattle headquarters
• Building partnership and understanding donor/partner context and landscape
• Providing social and cultural context
• Enhancing impact by influencing and shaping investments in coordination with foundation stakeholders.

What new agricultural initiatives is the Foundation undertaking in West Africa & Central Africa?
The Agricultural Development team at the Foundation has restructured their strategy. Our priority is for small-scale farmers and rural economies to thrive. We are now using a value chain approach, focusing on productivity improvements and the reduction of postharvest losses in specific staple crops and livestock, working closely with the governments of these countries and engaging stakeholders to get a complete sense of their agricultural work and plans. We are especially keen to work in areas that overlap with our strategy to achieve maximum leverage and address any major gaps that are impeding sustainable productivity growth in these value chains.

What are some of your challenges at work? What are the exciting highlights?
One of the key challenges to our involvement in the region is security. Violence and civil unrest, and unpredictability surrounding policies/politics in the region slow our momentum and disrupt plans.

The major highlight we have seen so far is that governments and existing players in the region are very welcoming. They are very willing to work with us and in most cases they see us not just as donors, but as thought partners.

Dr Valerie Bemo on a mission in Makindu. Photo from Bill & Melinda Gates Foundation.
Dr Valerie Bemo on a mission in Makindu. Photo from Bill & Melinda Gates Foundation.
What are some successful initiatives in agriculture and development in the region and their impacts?
It will take time to dramatically improve the productivity of small-scale farmers in the region, and it is too early for us to claim success in our own investments. This will require initiatives and collaboration from stakeholders. For instance, we believe that strong market incentives and a vibrant private sector involvement in agriculture are two very important factors for agriculture to thrive. The ultimate impact is to lift as many people out of poverty as possible, so focusing on the needs of the poorest farm families is also necessary.

As a partner, how would you describe the collaboration with IITA?
The partnership with IITA has been very good. With IITA’s work in some of the same priority crops and value chains, this collaboration may become even stronger. We are optimistic that our collaboration in the context of our new strategy will bring good results in Nigeria, and in the region as a whole.

What are some of the areas that IITA should focus more?
IITA priorities have been set out in the context of the reform of the international agricultural research centers, and we support that reform and those priorities.

How important is partnership in the African context? How could the collaboration among the various stakeholders be more effective?
Collaboration among all stakeholders in Africa will be very crucial for Africa to be able to tap into the incredible potential and increased agricultural productivity.

Any major breakthroughs in agriculture in the region will require collaboration from upstream research and development, to downstream adoption and scaling. It will require governments working with farmers, research institutions, private sector players and NGOs. Every group has the potential for making an important contribution, and a great variety of skills and resources are needed. We are optimistic that these critical players will achieve a new level of collaboration and sharing, leading to more efficiency and effectiveness.

What is your dream for African agriculture and development?
My dream for Africa is to see Africans leading the strategies and efforts to reduce poverty and to see the population, especially women and children, have access to basic health, education, clean drinking water and to be able to feed themselves. These will ultimately lead the people of Africa to having healthy and productive lives.

I fully share the Foundation’s “impatient optimist” vision for African agriculture development, that is to see productivity for 30 million farming households increase by 170% by 2030, with the ultimate goal of a 40% reduction in the $1/day poverty rate in the region. It is a big goal that will require not just our effort but that of all the major stakeholders, including IITA.