Wheat blast, caused by the fungus Magnaporthe oryzae pathotype Triticum, was first identified in 1985 in South America, but has been seen in Bangladesh in recent years. The expansion of the disease is a great concern for regions of similar environmental conditions in South Asia, and other regions globally.
Although management of the disease using fungicide is possible, it is not completely effective for multiple reasons, including inefficiency during high disease pressure, resistance of the fungal populations to some classes of fungicides, and the affordability of fungicide to resource-poor farmers. Scientists see the development and deployment of wheat with genetic resistance to blast as the most sustainable and farmer-friendly approach to preventing devastating outbreaks around the world.
In an article published in Nature Scientific Reports, a team of scientists from the International Maize and Wheat Improvement Center (CIMMYT) and partners, led by CIMMYT associate scientist Philomin Juliana, conducted a large genome-wide association study to look for genomic regions that could also be associated with resistance to wheat blast.
Using data collected over the last two years on CIMMYT’s International Bread Wheat Screening Nurseries (IBWSNs) and Semi-Arid Wheat Screening Nurseries (SAWSNs) by collaborators at the Bangladesh Wheat and Maize Research Institute (BWMRI) and the Instituto Nacional de Innovación Agropecuaria y Forestal (INIAF) in Bolivia, Philomin and fellow scientists found 36 significant markers on chromosome 2AS, 3BL, 4AL and 7BL that appeared to be consistently associated with blast resistance across different environments. Among these, 20 markers were found to be in the position of the 2NS translocation, a chromosomal segment transferred to wheat from a wild relative, Aegilops ventricosa, that has very strong and effective resistance to wheat blast.
The team also gained excellent insights into the blast resistance of the globally-distributed CIMMYT germplasm by genomic fingerprinting a panel over 4000 wheat lines for the presence of the 2NS translocation, and found that it was present in 94.1% of lines from IBWSN and 93.7% of lines from SAWSN. Although it is reassuring that such a high percentage of CIMMYT wheat lines already have the 2NS translocation and implied blast resistance, finding other novel resistance genes will be instrumental in building widespread, global resilience to wheat blast outbreaks in the long-term.
Read the publication by Philomin Juliana, Xinyao He, Muhammad R. Kabir, Krishna K. Roy, Md. Babul Anwar, Felix Marza, Jesse Poland, Sandesh Shrestha, Ravi P. Singh, and Pawan K. Singh
This work was made possible by the generous support of the Delivering Genetic Gains in Wheat (DGGW) project funded by the Bill & Melinda Gates Foundation, the U.K. Foreign, Commonwealth & Development Office (FCDO) and managed by Cornell University, the U.S. Agency for International Development’s Feed the Future initiative, the CGIAR Research Program on Wheat (WHEAT), the Indian Council of Agricultural Research (ICAR), The Swedish Research Council (Vetenskapsråd), and the Australian Centre for International Agricultural Research (ACIAR), #CIM/2016/219.
Wheat blast, a fast-acting and devastating fungal disease, has been reported for the first time on the African continent, according to a new article published by scientists from the Zambian Agricultural Research Institute (ZARI), the International Maize and Wheat Improvement Center (CIMMYT) and the US Department of Agriculture – Foreign Disease Weed Science Research Unit (USDA-ARS) in the scientific journal PLoS One.
Symptoms of wheat blast first appeared in Zambia during the 2018 rainy season in experimental plots and small-scale farms in the Mpika district, Muchinga province.
Wheat blast poses a serious threat to rain-fed wheat production in Zambia and raises the alarm for surrounding regions and countries on the African continent with similar environmental conditions. Worldwide, 2.5 billion consumers depend on wheat as a staple food, and in recent years, several African countries have been actively working towards reducing dependence on wheat imports.
“This presents yet another challenging biotic constraint to rain-fed wheat production in Zambia,” said Batiseba Tembo, wheat breeder at ZARI and lead scientist on the study.
A difficult diagnosis
“The first occurrence of the disease was very distressing. This happened at the spike stage, and caused significant losses,” said Tembo. “Nothing of this nature has happened before in Zambia.”
Researchers were initially confused when symptoms of the disease in the Mpika fields were first reported. Zambia has unique agro-climatic conditions, particularly in the rainfed wheat production system, and diseases such as spot blotch and Fusarium head blight are common.
“The crop had silvery white spikes and a green canopy, resulting in shriveled grains or no grains at all…Within the span of 7 days, a whole field can be attacked,” said Tembo. Samples were collected and analyzed in the ZARI laboratory, and suspicions grew among researchers that this may be a new disease entirely.
A history of devastation
Wheat blast, caused by Magnaporthe oryzae pathotype Triticum (MoT), was initially discovered in Brazil in 1985, and within decades had affected around 3 million hectares of wheat in South America alone. The disease made its first intercontinental jump to Asia in 2016, causing a severe outbreak in Bangladesh, reducing yield on average by as much as 51% in the affected fields.
The disease has now become endemic to Bangladesh, and has potential to expand to similar warm, humid and wet environments in nearby India and Pakistan, as well as other regions of favorable disease conditions.
Wheat blast spreads through infected seeds and crop residues as well as by spores that can travel long distances in the air. The spread of blast within Zambia is indicated by both mechanisms of expansion.
Developing expert opinions
Tembo participated in the Basic Wheat Improvement Course at CIMMYT in Mexico, where she discussed the new disease with Pawan Singh, head of Wheat Pathology at CIMMYT. Singh worked with Tembo to provide guidance and the molecular markers needed for the sample analysis in Zambia, and coordinated the analysis of the wheat disease samples at the USDA-ARS facility in Fort Detrick, Maryland.
All experiments confirmed the presence of Magnaporthe oryzae pathotype Triticum (MoT).
“This is a disaster which needs immediate attention,” said Tembo. “Otherwise, wheat blast has the potential to marginalize the growth of rain-fed wheat production in Zambia and may threaten wheat production in neighboring countries as well.”
A cause for innovation and collaboration
CIMMYT and the CGIAR Research Program on Wheat (WHEAT) are taking action on several fronts to combat wheat blast. Trainings, such as an international course led by the Bangladesh Wheat and Maize Research Institute (BWMRI) in collaboration with CIMMYT, WHEAT and others, invite international participants to gain new technical skills in blast diagnostics and treatment and understand different strategies being developed to mitigate the wheat blast threat. WHEAT scientists and partners are also working quickly to study genetic factors that increase resistance to the disease and develop early warning systems, among other research interventions.
“A set of research outcomes, including the development of resistant varieties, identification of effective fungicides, agronomic measures, and new findings in the epidemiology of disease development will be helpful in mitigating wheat blast in Zambia,” said Singh.
Tembo concluded, “It is imperative that the regional and global scientific community join hands to determine effective measures to halt further spread of this worrisome disease in Zambia and beyond.”
Financial support for this research was provided by the Zambia Agriculture Research Institute (ZARI), the CGIAR Research Program on Wheat (WHEAT), the Australian Centre for International Agricultural Research (ACIAR), and the US Department of Agriculture’s Agricultural Research Service (USDA-ARS).
The Basic Wheat Training Program and Wheat Blast Training is made possible by support from investors including ACIAR, WHEAT, the Indian Council of Agricultural Research (ICAR), Krishi Gobeshona Foundation (KGF), the Swedish Research Council (SRC) and the United States Agency for International Development (USAID).
About Accelerating Genetic Gains in Maize and Wheat for Improved Livelihoods
Accelerating Genetic Gains in Maize and Wheat for Improved Livelihoods (AGG) is a 5-year project that brings together partners in the global science community and in national agricultural research and extension systems to accelerate the development of higher-yielding varieties of maize and wheat — two of the world’s most important staple crops. Funded by the Bill & Melinda Gates Foundation, the UK Foreign, Commonwealth & Development Office (FCDO), the U.S. Agency for International Development (USAID) and the Foundation for Food and Agriculture Research (FFAR), AGG fuses innovative methods that improve breeding efficiency and precision to produce and deliver high-yielding varieties that are climate-resilient, pest- and disease-resistant, highly nutritious, and targeted to farmers’ specific needs.
The International Maize and What Improvement Center (CIMMYT) is the global leader in publicly-funded maize and wheat research and related farming systems. Headquartered near Mexico City, CIMMYT works with hundreds of partners throughout the developing world to sustainably increase the productivity of maize and wheat cropping systems, thus improving global food security and reducing poverty. CIMMYT is a member of the CGIAR System and leads the CGIAR programs on Maize and Wheat and the Excellence in Breeding Platform. The Center receives support from national governments, foundations, development banks and other public and private agencies. For more information visit www.cimmyt.org.
To build resilience against the threat of wheat blast, training sessions were held in Bangladesh to increase the reach of research findings and possible solutions as well as to educate the stakeholders involved. Since 2017, hands-on training on disease screening and surveillance of wheat blast have been organized every year in Bangladesh, with participation of national and international scientists. The third of its kind was jointly organized by the International Maize and Wheat Improvement Center (CIMMYT), Wheat and Maize Research Institute (BWMRI), and the Department of Agricultural Extension (DAE) Bangladesh during 19-28 February, 2019 at Regional Agricultural Research Station, Jashore with financial support from the Australian Centre for International Agricultural Research (ACIAR), the CGIAR Research Program on Wheat (WHEAT), the Indian Council of Agricultural Research (ICAR), the Krishi Gobeshona Foundation (KGF) and the U.S. Agency for International Development (USAID). The objective of the training was to learn the basic techniques of pathogen identification and its culturing, field inoculation and disease scoring and share experiences regarding combating the disease and its progress among the participants from home and abroad. Thirty five wheat scientists from China, India and Nepal as well as from BWMRI, DAE and CIMMYT in Bangladesh participated in the training.
The training was inaugurated by Kamala Ranjan Das, Additional Secretary (Research), Ministry of Agriculture, Bangladesh. The Director General of BWMRI, Dr. Naresh C. D. Barma was the Chair and Dr. T. P. Tiwari, Country Representative, CIMMYT Bangladesh and Additional Director of Jashore region of DAE were the special guests in the inaugural session. In addition to Bangladeshi experts, Dr. José Maurício C. Fernandes from Brazil, Dr. Pawan K. Singh from CIMMYT, Mexico and Dr. Timothy J. Krupnik from CIMMYT, Bangladesh presented the updates on the techniques for mitigating the disease. Dr. M. Akhteruzzaman, Deputy Director of DAE, Meherpur, who has been working very closely with wheat blast research and extension, spoke on the history and present status of wheat blast in Bangladesh. It was a unique opportunity for the trainees to listen from grass root level experience based on the real situation in the farmers’ fields.
Wheat is especially susceptible to blast infection during warm and humid weather conditions. While the fungus infects all above ground parts of the crop, infection in spikes is most critical and responsible for yield loss. Hence, to determine whether blast is endemic to the specific region and also to assess the epidemic potential in unaffected regions, Dr. Fernandes developed a wheat blast forecasting model with support from CIMMYT Bangladesh. To collect data on the presence of wheat blast spores in the air, CIMMYT, in collaboration with BWMRI, installed four spore traps in four different wheat fields in Meherpur, Faridpur, Rajshahi and Dinajpur districts of Bangladesh. The results from these spore traps and weather parameters will help validate the wheat blast forecasting model. After final validation, the recommendation message will be sent to farmers and DAE personnel through mobile app. This will help farmers decide the perfect time for spraying fungicide to control blast effectively.
During the training participants received the hands-on experience of activities in the precision phenotypic platform (PPP) for wheat blast, where 4500 germplasm from different countries of the world and CIMMYT Mexico are being tested under artificial inoculated conditions. To keep the environment sufficiently humid, the trial is kept under mist irrigation to facilitate proper disease development. Trainees learned identification of leaf and spike symptoms of wheat blast, identification and isolation of conidia under microscope, inoculum preparation, tagging selected plants in the fields for inoculation, field inoculation of germplasms being tested at the PPP and more.
According to the United States Department of Agriculture (USDA), wheat consumption in Bangladesh is 7.7 million tons as of 2018 while only 1.25 million tons are supplied domestically. Since the majority of wheat is imported, it will adversely affect the economy if the comparatively smaller amount the country produces decreases due to blast. So the impact of wheat blast is not limited to food production but affects the economy as a whole, and steps to help mitigate the disease are crucial in ensuring healthy growth of wheat yield.
Wheat blast, caused by Magnaporthe oryzae pathotype Triticum (MoT), was first discovered in Brazil in 1985 and then surprisingly appeared in the wheat fields of Bangladesh in 2016, causing 25-30% yield loss in 15,000 ha. As an immediate response to this crisis, CIMMYT and the government of Bangladesh have worked together to mitigate the disease, most notably by distributing factsheets to farmers, conducting routine follow-ups followed by the development and rapid release of blast resistant wheat variety BARI Gom 33 and tolerant varieties (BARI Gom 30 and 32) and strengthening research on blast.