For a decade, scientists at the International Maize and Wheat Improvement Center (CIMMYT) have been at the forefront of a multidisciplinary and multi-institutional effort to contain and effectively manage maize lethal necrosis (MLN) disease in Africa.
The manual is relevant to stakeholders in countries where MLN is already present, and also aims to offer technical tips to ââhigh-riskâ countries globally for proactive implementation of practices that can possibly prevent the incursion and spread of the disease,â writes B.M. Prasanna, director of CIMMYTâs Global Maize Program and MAIZE, in the foreword.
âWhile intensive multi-disciplinary and multi-institutional efforts over the past decade have helped in containing the spread and impact of MLN in sub-Saharan Africa, we cannot afford to be complacent. We need to continue our efforts to safeguard crops like maize from devastating diseases and insect-pests, and to protect the food security and livelihoods of millions of smallholders,â says Prasanna, who is presently leading the OneCGIAR Plant Health Initiative Design Team.
A CIMMYT technician cuts a leaf sample for DNA extraction. (Photo: CIMMYT)
Wheat breeders from across the globe took a big step towards modernizing their molecular breeding skills at a recent workshop sponsored by the Wheat Initiative, with the CGIAR Excellence in Breeding Platform (EiB) and the International Maize and Wheat Improvement Center (CIMMYT).
The workshop focused on three open-source tools used in molecular breeding: GOBii-GDM for genomic data management, Flapjack for data visualization and breeding analysis, and Galaxy for Genomic Selection. These tools help breeders make selections more quickly and precisely, and ultimately lead to more cost effective and efficient improvement of varieties.
The Wheat Initiative â a global scientific collaboration whose goals are to create improved wheat varieties and disseminate better agronomic practices worldwide â and its Breeding Methods and Strategies expert working group had planned to host these trainings during the 2020 Borlaug Global Rust Initiative Technical Workshop in the United Kingdom. After it became obvious that in-person trainings were not possible, the course organizers â including CIMMYT molecular wheat breeder Susanne Dreisigacker and EiB Adoption Lead and former GOBii project director Elizabeth Jones â decided to come together to host online workshops.
Many of the tools will be incorporated into EiBâs Enterprise Breeding System (EBS), a new integrated data management system being developed for CGIAR breeders. Jones plans to also design training modules for these molecular breeding tools that will be accessible to anyone through the EiB Toolbox.
The first session of the workshop âTransforming Wheat Breeding Through Integrated Data Management with GOBii and Analysis in Flapjackâ benefited breeders from Australia, Canada, Ethiopia, France, India, Ireland, Italy, Morocco, Pakistan, Switzerland, Tunisia, the United Kingdom and the United States.
Susanne Dreisigacker presents during one of the sessions of the workshop.
Powering data analysis around the world
The workshop series, âTransforming Wheat Breeding Through Integrated Data Management with GOBii and Analysis in Flapjack,â aimed to benefit breeders from wheat producing countries all over the world, with sessions over two different time zones spread out over three days to reduce âZoom fatigue.â Participants joined the first session from Australia, Canada, Ethiopia, France, India, Ireland, Italy, Morocco, Pakistan, Switzerland, Tunisia, the United Kingdom and the United States.
âIt was wonderful to see the diversity of participants that we were able to train through an online workshop, many of whom otherwise might not have been able to travel to the UK for the original meeting,â said Jones. âParticipants were very engaged, making the workshop so rewarding.â
The workshop was guided by Teresa Saavedra, Wheat Initiative coordinator. Apart from Dreisigacker and Jones, other trainers explained specific tools and approaches. Iain Milne from the James Hutton Institute in Scotland gave more details about the Flapjack genotyping visualization tool, which includes analysis for pedigree verification, marker assisted backcrossing and forward breeding. Andrew Kowalczyk, developer at Diversity Arrays Technology, spoke about the genotyping data QC tool DArTView.
A CIMMYT technician performs one of the steps to extract DNA samples from plants. (Photo: CIMMYT)
Clay Sneller, wheat breeder at Ohio State University, contributed training materials for important molecular breeding tools. Carlos Ignacio, previously based at the International Rice Research Center (IRRI) and now working on a PhD in Genomic Selection at Ohio State University, contributed his experience as a GOBii team member and a major contributor towards the design of Flapjack tools. Star Gao, application specialist with GOBii and now a requirements analyst for the Enterprise Breeding System, also facilitated the sessions.
Gilles Charmet, research director at the Franceâs National Research Institute for Agriculture, Food and Environment (INRAE), introduced the sessions in the Americas/Europe time zone with welcome remarks and overview of the goals of the Wheat Initiative. Alison Bentley, director of the CIMMYT Global Wheat Program, briefed on the achievements and goals of the CIMMYT Wheat program and the Accelerating Genetic Gains in Maize and Wheat for Improved Livelihoods (AGG) project.
âThis training will contribute towards us reaching our AGG goals of accelerating gains in wheat, by sharing technical knowledge, and allowing our beneficiary partners to have state-of-the-art know-how in the use of genetic and genomic data,â Bentley said.
The sessions continue in Australasia next week, and will be introduced by Peter Langridge, chair of the Scientific Board for the Wheat Initiative, and EiB director Michael Quinn. Sanjay Kumar Singh, incoming chair of the Breeding expert working group for the Wheat Initiative, will close the event.
The outbreak of maize lethal necrosis (MLN) disease in east Africa in 2011 (first reported in Kenyaâs South Rift Valley) was a major concern, given that maize is the regionâs most important staple crop. This disease is caused by co-infection of plants with two viruses â maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV) â and can cause yield losses of up to 90%. It spread rapidly across east Africa, compromising food and economic security for several million smallholder farmers.
MLN is a complex challenge that must be addressed through a multipronged approach. While significant advances have been made through intensive efforts by CIMMYT and other partners in terms of identifying and developing MLN tolerant or resistant hybrids, the rapid spread of the epidemic over the last few years remains a concern for farming communities, policy makers, national plant protection organization and the commercial seed sector, as well as the international scientific community.
There is also increasing suspicion that commercial seed flows may have been the initial source of the dissemination of the MLN-causing viruses over large distances, and it is thought that transmission of MCMV through contaminated maize seed continues to be a major risk factor in the spread of MLN across east Africa and beyond. However, there is a lack of reliable information on various aspects of MLN epidemiology, including the rate of MCMV transmission through seed.
The project on âPreventing Seed Transmission of Maize Lethal Necrosis in Africaâ aims to generate a better understanding of these epidemiological issues to allow for more effective control of MCMV transmission through commercial seed, support the development of effective, evidence-based phytosanitary regulations, reduce MLN disease pressure in eastern Africa, and curb the spread to non-endemic countries in other parts of the continent.
Objectives
Develop appropriate protocols for assessing MLN transmission through seed
Develop reliable and cost-effective diagnostic protocols for curbing the spread of MCMV/MLN through seed implemented by NPPOs and commercial seed companies.
Determine the rates of transmission for the East African and US (Hawaiian) isolates of MCMV in tropical, subtropical and temperate maize germplasm
Understand the mode of MCMV transmission through commercial seed within endemic areas to allow more effective control
Determine the distribution of MCMV in maize seed, and the effects of seed treatments on virus transmission
Identify economical treatment methods to reduce or prevent MCMV transmission through seed for commercial seed industry and casual seed trade
Generate detailed understanding of the role of root debris on persistence of MCMV in the soil, the persistence of the virus in different soil types, and the duration of virus viability in the soil
Disseminate science-based knowledge and evidence generated through this project to National Plant Protection Organizations (NPPOs) and Ministries of Agriculture in sub-Saharan Africa
Itâs been eight years since maize lethal necrosis (MLN) was first reported on the African continent. When it appeared in Kenyaâs Bomet County in 2011, a sense of panic swept across the maize sector. Experts quickly realized that all maize varieties on the market were susceptible to this viral disease, which could wipe out entire maize fields.
Spearheaded by the International Maize and Wheat Improvement Center (CIMMYT), a rapid regional response involving national agriculture research systems (NARS), national plant protection organizations and seed sector partners was set up. The response involved multiple approaches: rigorous surveillance, epidemiology research, disease management across the seed value chain, and screening and fast-tracking of the MLN-tolerant maize breeding program.
Now, CIMMYT and its partners are reflecting on the tremendous impact of transboundary coalition to contain the devastating disease.
âCountry reports show there are now much less incidents of MLN in the region. We have effectively contained this disease as no new country in sub-Saharan Africa reported MLN since Ethiopia in 2014. This is a great achievement of an effective public private partnership,â noted B.M. Prasanna, Director of CIMMYT’s Global Maize Program and the CGIAR Research Program on Maize.
He was speaking at the closure workshop for the MLN Diagnostics and Management project and the MLN Epidemiology project on October 15-17, 2019, in Nairobi, Kenya. Experts from research, plant health and seed sector organizations from eastern and southern Africa reflected on the tremendous impact of the transboundary coalition to contain MLN across the region.
âThe outbreak of the disease in Uganda in 2012 was a huge challenge as all the maize varieties and hybrids on the market were susceptible. With the support of CIMMYT and other partners in the national agriculture research systems, we got access to Bazooka, a high-yielding, drought- and MLN-tolerant maize variety that has helped in containing the disease,â said Godfrey Katwere, marketing manager for NASECO.
Until now, 19 MLN-tolerant and -resistant hybrids have been released, helping to keep the disease away from farmersâ fields and to stop its spillover to non-endemic countries in sub-Saharan Africa.
CIMMYT team members check for traces of the maize chlorotic mottle virus (MCMV) in maize plants during a visit to the MLN screening facility in Naivasha, Kenya. (Photo: Joshua Masinde/CIMMYT)
Science in action
The MLN screening facility, established in Naivasha in 2013, has been key to a better understanding of the disease and to setting up MLN hybrid tolerance and resistance breeding efforts. The facility, funded by the Bill & Melinda Gates Foundation and the Syngenta Foundation for Sustainable Agriculture, has supported public and private partners to screen over 200,000 germplasm with around 300,000 rows of maize.
State-of-the-art epidemiology research has been carried out to identify how the disease could be transmitted and the best diagnostics methods along the seed value chain.
MLN is caused by the combination of the maize chlorotic mottle virus (MCMV) and any of the viruses belonging to the Potyviridae family.
As part of the project, studies showed that moist soil had higher MCMV virus loads than dry soil. The studies â conducted by Benham Lockhart of University of Minnesota and Peg Redinbaugh, a professor at Ohio State University and Research Leader and Research Plant Molecular Geneticist at USDA â indicated that MCMV can stay active in runoff water, and helped in understanding how the disease is transmitted and how to define management protocols.
âCrop debris may also act as source of MCMV inoculum but for a limited period of up to two months,â said L.M. Suresh, CIMMYT Maize Pathologist, in reference to soil transmission studies conducted by CIMMYT. âA host-free period of two months is, therefore, recommended for effective management of MLN,â he noted.
Rapid and low-cost MLN-causing virus detection methods such as immunostrips and ELISA-based tests were adopted at scale.
âAfter optimizing the protocols for MLN virusesâ diagnosis suitable for African systems, we transferred these technologies to [national plant protection organizations] and seed companies, not just within the endemic countries but also to the non-endemic countries in southern and west Africa, through intensive trainings,â Prasanna explained. âWe created a digital MLN surveillance tool under the Open Data Kit (ODK) app for NPPOs and other stakeholders to effectively carry out MLN surveillance on the ground. The survey information is captured in real time in farmersâ and seed production fields coupled with rapid immunostrips MLN tests,â he remarked.
According to Francis Mwatuni, Project Manager of the MLN Diagnostics and Management project, this proactive and collaborative surveillance network has been an important outcome that helped curb MLN from spreading to non-endemic regions. âIn 2016, we only had 625 surveillance points. By 2019, the surveillance points in all the target countries stood at 2,442, which intensified the alertness on MLN presence and how to effectively deal with it,â Mwatuni said. In total, 7,800 surveillance points were covered during the project implementation period.
Over 100 commercial seed firms have also been trained on how to produce MLN-free seed to facilitate trade within the endemic nations and to ensure the disease is not transferred to the non-endemic countries via contaminated seeds.
Participants at the MLN projects closure workshop stand for a group photo. (Photo: Joshua Masinde/CIMMYT)
Sustaining the fight
Researchers continue to work to lessen MLNâs resurgence or new outbreaks. In 2018, incidents in all endemic countries, except Ethiopia, declined sharply. One suggested explanation for the upsurge in Ethiopia, especially in the northwestern region, was reduced use of pesticide for fall armyworm control, as compared to previous years where heavy application of these pesticides also wiped out MLN insect vectors, such as maize thrips and aphids.
At the end of the projects, partners urged for the scale-up of second-generation MLN-tolerant and -resistant varieties. They explained farmers would fully benefit from recent genetic gains of the new improved varieties and its protection against MLN.
âDespite the success registered, MLN is still a major disease requiring constant attention. We cannot rest as we redirect our energies at sustaining and building on the gains made,â said Beatrice Pallangyo, principal agricultural officer in Tanzaniaâs Ministry of Agriculture, Food Security and Cooperatives.
After the success containing MLN, stakeholders suggested the need to stay alert on other transboundary pests and diseases such as the tar spot complex, which could be a major threat to Africaâs food security in case of an outbreak.
