Wheat blast: A fungus that spread to three continents can threaten food security globally

Magnaporthe oryzae fungus was first reported in South America, from where it independently spread to Asia and Africa

By Lalit Maurya
Published: Tuesday 18 April 2023
Magnaporthe oryzae infects wild and cultivated grasses, most notably rice and wheat. Photo for representation: iStock
Magnaporthe oryzae infects wild and cultivated grasses, most notably rice and wheat. Photo for representation: iStock Magnaporthe oryzae infects wild and cultivated grasses, most notably rice and wheat. Photo for representation: iStock

Could the next pandemic affect global food security? Scientists have warned that the fungus Magnaporthe oryzae, which is destroying South American wheat crops, could spread worldwide. The pathogen affects the crop in a disease known as ‘wheat blast’. 

The seriousness of the disease is indicated by the fact that crops are burnt to avoid this disease. Magnaporthe oryzae originated in South America, but cases of infection have also been reported in Asia in 2016 and Africa in 2018. 

Genomic analysis of fungus samples from all three continents showed that these fungi are part of the same family. This research’s results were published on April 11, 2023 in the journal Plos Biology.

Wheat crops around the world are susceptible to the fungus, the researchers warned in the study. The pathogen is also resistant to fungicides. The biggest concern is that this fungus has the potential to affect not only wheat but also other major food crops.

“This is a very serious disease; it threatens wheat cultivation in some of the poorest parts of the world,” study co-author Nick Talbot, a plant pathologist at the Sainsbury Laboratory in Norwich, UK, said at a press briefing. It also can spread throughout the world, he added. 

Need for accurate, early detection

Genomic surveillance allows for early and accurate detection of these, which can lead to the discovery of the origin of the disease and help create a prevention strategy. 

Magnaporthe oryzae infects wild and cultivated grasses, most notably rice and wheat. Researchers first detected the pathogen in Brazilian wheat crops in the 1980s. The fungus has since spread throughout South America. In some areas, the situation became so severe that the fungus destroyed the entire crop.

How wheat blast destroys crops

Source: International Maize and Wheat Improvement Center, known by its Spanish acronym, CIMMYT

After this, Asia’s first outbreak of this pathogenic wheat blast was reported in Bangladesh in 2016. Wheat blast led to a loss of 51 per cent in crop yield that year. 

Two years later, an outbreak of this fungus was detected in wheat crops in Zambia, which was the first time the pathogen was detected in Africa. However, it is not clear whether it reached Zambia from Bangladesh or South America.

In the recently published study, scientists analysed more than 500 samples of the fungus to understand the origin of the pathogen.

Separate genome sequencing of 71 samples also helped identify that wheat blast fungus detected in Bangladesh in 2016 and Zambia in 2018 belonged to different branches of the disease lineage from South America. 

This suggests that the strain of wheat blast from South America independently reached Africa and Asia, said Hernan Burbano, geneticist at the University College London and researcher associated with the study. Therefore, humans are likely transporting these pathogens somehow. 

Importing infected seeds is a possible outbreak source, the study said. Before the outbreak in Bangladesh, the country had received a large quantity of wheat seeds from Brazil. However, this doesn’t help accurately identify its origin as the fungus lineage was found in Brazil as well as in Bolivia.

Researchers are now using genomic information to monitor the spread of wheat blast throughout Bangladesh, Tofazzal Islam, an ecological chemist at Bangabandhu Sheikh Mujibur Rahman Agricultural University in Gazipur, Bangladesh, said at a press briefing.

Islam’s team is also using the insights obtained to breed wheat crops resistant to the pathogen lineage behind the epidemic.

Genomic analysis has highlighted the dangers associated with the fungus. Research has shown that the fungus responsible for the outbreak is susceptible to certain fungicides, but laboratory experiments have shown that resistance can arise through spontaneous mutations.

According to the research, the strain developed by self-cloning can acquire new characteristics by mixing with another genus of the fungus. The researchers found that the wheat blast strain may have interbred with another strain infecting millet crops in Africa.

The average yield loss due to pests and diseases in wheat crop is more than 21 per cent, according to another study. Above all, changes in climate and rainfall patterns and increase in temperatures are also causing heavy damage to crops, suggesting an impending crisis of food security.

Crores of people can reach the brink of starvation due to a combined effect of these factors. In such a situation, efforts should be made to eliminate this pathogenic wheat blast before it is too late, the researchers suggested. 

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