Written by Bea Ciordia on . Posted in Uncategorized.
The Managing Wheat Blast in Bangladesh: Identification and Introgression of Wheat Blast Resistance for Rapid Varietal Development and Dissemination project aims to characterize novel sources of wheat blast resistance, identification, and molecular mapping of resistance loci/gene(s) and their introgression into varietal development pipelines for rapid dissemination of resistant varieties in Bangladesh.
Objectives
Validate the effects of genes Rmg1, Rmg8 and RmgGR119 in field experiments
Identify novel wheat blast resistant sources and generating the corresponding genetic materials for investigating the resistance Quantitative Trait Loci (QTL)/genes
Monitor the adoption of resistant varieties BARI Gom 33 and WMRI Gom 3 by women and men farmers to learn the drivers and obstacles that are involved in the process, to inform the design of a farmer-preferred product profile, and factors in impact pathway
Build the capacity of the Bangladesh Wheat and Maize Research Institute (BWMRI) to operate major infrastructure in Jashore and Dinajpur at the individual and institutional levels
Enhance collaboration between Bangladesh and other countries showing interest on wheat blast
Train young wheat researchers and breeders in Jashore Precision Phenotyping Platform (PPP)
Genomic selection identifies individual plants based on the information from molecular markers, DNA signposts for genes of interest, that are distributed densely throughout the wheat genome. For wheat blast, the results can help predict which wheat lines hold promise as providers of blast resistance for future crosses and those that can be advanced to the next generation after selection.
In this study, scientists from the International Maize and Wheat Improvement Center (CIMMYT) and partners evaluated genomic selection by combining genotypic data with extensive and precise field data on wheat blast responses for three sets of genetically diverse wheat lines and varieties, more than 700 in all, grown by partners at locations in Bangladesh and Bolivia over several crop cycles.
The study also compared the use of a small number of molecular markers linked to the 2NS translocation, a chromosome segment from the grass species Aegilops ventricosa that was introduced into wheat in the 1980s and is a strong and stable source of blast resistance, with predictions using thousands of genome-wide markers. The outcome confirms that, in environments where wheat blast resistance is determined by the 2NS translocation, genotyping using one-to-few markers tagging the translocation is enough to predict the blast response of wheat lines.
Finally, the authors found that selection based on a few wheat blast-associated molecular markers retained 89% of lines that were also selected using field performance data, and discarded 92% of those that were discarded based on field performance data. Thus, both marker-assisted selection and genomic selection offer viable alternatives to the slower and more expensive field screening of many thousands of wheat lines in hot-spot locations for the disease, particularly at early stages of breeding, and can speed the development of blast-resistant wheat varieties.
The research was conducted by scientists from the International Maize and Wheat Improvement Center (CIMMYT), the Bangladesh Wheat and Maize Research Institute (BWMRI), the Instituto Nacional de Innovación Agropecuaria y Forestal (INIAF) of Bolivia, the Borlaug Institute for South Asia (BISA) and the Indian Council of Agricultural Research (ICAR) in India, the Swedish University of Agricultural Sciences (Alnarp), and Kansas State University in the USA. Funding for the study was provided by the Bill & Melinda Gates Foundation, the Foreign and Commonwealth Development Office of the United Kingdom, the U.S. Agency for International Development (USAID), the CGIAR Research Program on Wheat (WHEAT), the Indian Council of Agricultural Research (ICAR), the Swedish Research Council, and the Australian Centre for International Agricultural Research (ACIAR).
Cover photo: A researcher from Bangladesh shows blast infected wheat spikes and explains how the disease directly attacks the grain. (Photo: Chris Knight/Cornell University)
As wheat blast continues to infect crops in countries around the world, researchers are seeking ways to stop its spread. The disease — caused by the Magnaporthe oryzae pathotype Triticum — can dramatically reduce crop yields, and hinder food and economic security in the regions in which it has taken hold.
Researchers from the International Maize and Wheat Improvement Center (CIMMYT) and other international institutions looked into the potential for wheat blast to spread, and surveys existing tactics used to combat it. According to them, a combination of methods — including using and promoting resistant varieties, using fungicides, and deploying strategic agricultural practices — has the best chance to stem the disease.
The disease was originally identified in Brazil in 1985. Since then, it has spread to several other countries in South America, including Argentina, Bolivia and Paraguay. During the 1990s, wheat blast impacted as many as three million hectares in the region. It continues to pose a threat.
Through international grain trade, wheat blast was introduced to Bangladesh in 2016. The disease has impacted around 15,000 hectares of land in the country and reduced average yields by as much as 51% in infected fields.
Because the fungus’ spores can travel on the wind, it could spread to neighboring countries, such as China, India, Nepal and Pakistan — countries in which wheat provides food and jobs for billions of people. The disease can also spread to other locales via international trade, as was the case in Bangladesh.
“The disease, in the first three decades, was spreading slowly, but in the last four or five years its pace has picked up and made two intercontinental jumps,” said Pawan Singh, CIMMYT’s head of wheat pathology, and one of the authors of the recent paper.
In the last four decades, wheat blast has appeared in South America, Asia an Africa. (Video: Alfonso Cortés/CIMMYT)
The good fight
Infected seeds are the most likely vector when it comes to the disease spreading over long distances, like onto other continents. As such, one of the key wheat blast mitigation strategies is in the hands of the world’s governments. The paper recommends quarantining potentially infected grain and seeds before they enter a new jurisdiction.
Governments can also create wheat “holidays”, which functionally ban cultivation of wheat in farms near regions where the disease has taken hold. Ideally, this would keep infectable crops out of the reach of wheat blast’s airborne and wind-flung spores. In 2017, India banned wheat cultivation within five kilometers of Bangladesh’s border, for instance. The paper also recommends that other crops — such as legumes and oilseed — that cannot be infected by the wheat blast pathogen be grown in these areas instead, to protect the farmers’ livelihoods.
Other tactics involve partnerships between researchers and agricultural workers. For instance, early warning systems for wheat blast prediction have been developed and are being implemented in Bangladesh and Brazil. Using weather data, these systems alert farmers when the conditions are ideal for a wheat blast outbreak.
Researchers are also hunting for wheat varieties that are resistant to the disease. Currently, no varieties are fully immune, but a few do show promise and can partially resist the ailment depending upon the disease pressure. Many of these resistant varieties have the CIMMYT genotype Milan in their pedigree.
“But the resistance is still limited. It is still quite narrow, basically one single gene,” Xinyao He, one of the co-authors of the paper said, adding that identifying new resistant genes and incorporating them into breeding programs could help reduce wheat blast’s impact.
Wheat spikes damaged by wheat blast. (Photo: Xinyao He/CIMMYT)
The more the merrier
Other methods outlined in the paper directly involve farmers. However, some of these might be more economically or practically feasible than others, particularly for small-scale farmers in developing countries. Wheat blast thrives in warm, humid climates, so farmers can adjust their planting date so the wheat flowers when the weather is drier and cooler. This method is relatively easy and low-cost.
The research also recommends that farmers rotate crops, alternating between wheat and other plants wheat blast cannot infect, so the disease will not carry over from one year to the next. Farmers should also destroy or remove crop residues, which may contain wheat blast spores. Adding various minerals to the soil, such as silicon, magnesium, and calcium, can also help the plants fend off the fungus. Another option is induced resistance, applying chemicals to the plants such as jasmonic acid and ethylene that trigger its natural resistance, much like a vaccine, Singh said.
Currently, fungicide use, including the treatment of seeds with the compounds, is common practice to protect crops from wheat blast. While this has proven to be somewhat effective, it adds additional costs which can be hard for small-scale farmers to swallow. Furthermore, the pathogen evolves to survive these fungicides. As the fungus changes, it can also gain the ability to overcome resistant crop varieties. The paper notes that rotating fungicides or developing new ones — as well as identifying and deploying more resistant genes within the wheat — can help address this issue.
However, combining some of these efforts in tandem could have a marked benefit in the fight against wheat blast. For instance, according to Singh, using resistant wheat varieties, fungicides, and quarantine measures together could be a time-, labor-, and cost-effective way for small-scale farmers in developing nations to safeguard their crops and livelihoods.
“Multiple approaches need to be taken to manage wheat blast,” he said.
Wheat blast damages wheat spikes. (Photo: Xinyao He / CIMMYT)
In an article published in Nature Scientific Reports, a team of scientists led by wheat breeder Philomin Juliana from the International Wheat and Maize Improvement Center (CIMMYT) conducted a large genome-wide association study to look for genomic regions that could also be associated with resistance to wheat blast.
Juliana 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 4,000 wheat lines for the presence of the 2NS translocation, and found that it was present in 94.1% of lines from International Bread Wheat Screening Nurseries (IBWSNs) and 93.7% of lines from Semi-Arid Wheat Screening Nurseries (SAWSNs). 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.
The researchers used data collected over the last two years from CIMMYT’s IBWSNs and SAWSNs by collaborators at the Bangladesh Wheat and Maize Research Institute (BWMRI) and Bolivia’s Instituto Nacional de Innovación Agropecuaria y Forestal (INIAF).
Devastating fungal disease
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.
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).
Wheat blast is a fast-acting and devastating fungal disease that threatens food safety and security in tropical areas in South America and South Asia. Directly striking the wheat ear, wheat blast can shrivel and deform the grain in less than a week from the first symptoms, leaving farmers no time to act.
The disease, caused by the fungus Magnaporthe oryzae pathotype triticum (MoT), can spread through infected seeds and survives on crop residues, as well as by spores that can travel long distances in the air.
Magnaporthe oryzae can infect many grasses, including barley, lolium, rice, and wheat, but specific isolates of this pathogen generally infect limited species; that is, wheat isolates infect preferably wheat plants but can use several more cereal and grass species as alternate hosts. The Bangladesh wheat blast isolate is being studied to determine its host range. The Magnaporthe oryzae genome is well-studied but major gaps remain in knowledge about its epidemiology.
The pathogen can infect all aerial wheat plant parts, but maximum damage is done when it infects the wheat ear. It can shrivel and deform the grain in less than a week from first symptoms, leaving farmers no time to act.
Where is wheat blast found?
First officially identified in Brazil in 1985, the disease is widespread in South American wheat fields, affecting as much as 3 million hectares in the early 1990s. It continues to seriously threaten the potential for wheat cropping in the region.
In 2016, wheat blast spread to Bangladesh, which suffered a severe outbreak. It has impacted around 15,000 hectares of land in eight districts, reducing yield on average by as much as 51% in the affected fields.
Wheat-producing countries and presence of wheat blast.
How does blast infect a wheat crop?
Wheat blast spreads through infected seeds, crop residues as well as by spores that can travel long distances in the air.
Blast appears sporadically on wheat and grows well on numerous other plants and crops, so rotations do not control it. The irregular frequency of outbreaks also makes it hard to understand or predict the precise conditions for disease development, or to methodically select resistant wheat lines.
At present blast requires concurrent heat and humidity to develop and is confined to areas with those conditions. However, crop fungi are known to mutate and adapt to new conditions, which should be considered in management efforts.
How can farmers prevent and manage wheat blast?
There are no widely available resistant varieties, and fungicides are expensive and provide only a partial defense. They are also often hard to obtain or use in the regions where blast occurs, and must be applied well before any symptoms appear — a prohibitive expense for many farmers.
The Magnaporthe oryzae fungus is physiologically and genetically complex, so even after more than three decades, scientists do not fully understand how it interacts with wheat or which genes in wheat confer durable resistance.
Researchers from the International Maize and Wheat Improvement Center (CIMMYT) are partnering with national researchers and meteorological agencies on ways to work towards solutions to mitigate the threat of wheat blast and increase the resilience of smallholder farmers in the region. Through the USAID-supported Cereal Systems Initiative for South Asia (CSISA) and Climate Services for Resilient Development (CSRD) projects, CIMMYT and its partners are developing agronomic methods and early warning systems so farmers can prepare for and reduce the impact of wheat blast.
CIMMYT works in a global collaboration to mitigate the threat of wheat blast, funded by the Australian Centre for International Agricultural Research (ACIAR), the CGIAR Research Program on Wheat (WHEAT), the Indian Council of Agricultural Research (ICAR) and the Swedish Research Council (Vetenskapsrådet). Some of the partners who collaborate include the Bangladesh Wheat and Maize Research Institute (BWMRI), Bolivia’s Instituto Nacional de Innovación Agropecuaria y Forestal (INIAF), Kansas State University and the Agricultural Research Service of the US (USDA-ARS).
