Study links climate change with wheat blast; warns crop yield could drop by 75% in South America, Africa by 2050

A new study has warned of links between warming climate and the devastating fungal plant disease wheat blast. The disease currently poses a threat to 6.4 million hectares and by 2050, climate change is likely make the situation worse and threaten 13.5 million hectares of cropland, the study warned. 

Wheat blast alone has the potential to cut wheat production worldwide by 13 per cent. However, the study cautioned that other effects of climate change could cause yields to fall even further. 

The analysis focused exclusively on nations with wheat growing areas and covered 86 countries across six continents — Africa, North America, South America, Europe and Asia.

South America and Africa will be the most vulnerable regions to wheat blast in the future climate, with up to 75 per cent of their wheat acreage at risk by 2050, warned the team of researchers from institutes International Maize and Wheat Improvement Center (also known as CIMMYT), Brazilian Agricultural Research Corporation, University of Florida, International Food Policy Research Institute and Technical University Munich. 

Potential wheat yield loss from wheat blast simulated for climate change scenarios for 2040–2070

These areas are among the most vulnerable to the direct impacts of climate change, where food security is already a considerable concern and wheat consumption is increasing, especially in urban areas. 

By 2050, there will be more wheat blast-prone locations due to a confluence of factors, including increasing temperatures and persistent leaf moisture, which foster the growth and dissemination of the pathogen. 

This is of concern since the fungus has the potential to affect not only wheat but also other major food crops.

Wheat blast is a fungal disease for warm and humid wheat production regions, caused by the pathogen Magnaporthe oryzae pathotype Triticum (MoT). The pathogen can cause total losses to wheat producers during outbreak years. For example, the disease was detected in 70 counties in State of Paraná, Brazil and caused up to 100 per cent yield losses in commercial fields in 1987.

The devastating wheat blast outbreak was first reported in Brazil in 1985. The disease was restricted to South America until 2016, when a series of grain imports from Brazil led to a wheat blast outbreak in Bangladesh.

WHEAT BLAST OUTBREAKS THROUGH THE YEARS

Climate change-induced temperature increase probably contributed to the wheat blast epidemic in Bangladesh and will drive future occurrences in new countries, the global crop simulation study said, showing the potential global risk associated with the spread of wheat blast.

A study published in 2018 too revealed that all the severe epidemics of wheat blast occurring across South America and Asia during the wet and warm years of 1987, 1997, 2002, 2009, 2012 and 2015 coincided with weather conditions dominated by the El Nino phenomenon.

Wheat blast could expand to new, unaffected geographies 

In South America, the wheat blast disease is already present. But the disease could further expand mainly in countries that already suffer losses due to the disease, including Brazil, Argentina, Bolivia and Paraguay. It could also affect Uruguay, which has not been affected by the pest so far, the study said.

In 2020, the pathogen emerged in Zambia for the first time in Africa, and the study warned it may further expand in the country. Ethiopia, Kenya and Congo too are vulnerable and may suffer from yield losses due to wheat blast.

In Oceania and North America, only a small portion of wheat-growing area is currently vulnerable to wheat blast. However, the changing climate may expand it to 5 per cent and 12 per cent of the total wheat area of these countries, respectively. 

The projections further suggested that the presence of wheat blast may also increase in the United States and Mexico. In Oceania, the disease may spread to New Zealand, which has not been affected so far 

Previously unaffected countries —  Japan, Italy, Spain and New Zealand — in the Asian, European and Oceania region, respectively, may also be impacted. 

It may expand into southeast China, potentially incurring yield losses. Recent studies strongly suggested that MoT has the potential to spread into the country with rising temperatures.

In India, some parts of the country may become less vulnerable to wheat blast if dry seasonal conditions with more frequent severe high temperatures (over 35 degrees Celsius) occur in the later half of the wheat-growing season in future climates, the paper said. Although the risk of wheat blast infection is decreased by such high temperatures, they also create terminal heat stress, which lowers the country’s potential output.

The cold climate in Europe and other countries where snow falls reduces the probability of infection. But climate change will potentially alter the distribution of different insect pests and diseases over time, the study warned.

It is possible for European places near the Mediterranean to experience a favourable climate for the fungal infection. This includes Italy and parts of southern France and Spain, alerted the paper.

Adapting to wheat blast as climate changes 

Given the threat to important wheat-growing areas around the world from wheat blast, farmers may need to shift to less susceptible crops to mitigate production and financial losses, suggested the study. 

It suggested multiple strategies to manage the disease, citing examples of the countries affected. For instance, maize cultivation is gradually replacing wheat in midwest Brazil. Breeding blast-resistant wheat is also a very important strategy that could mitigate future losses in new vulnerable areas and has already been initiated, it said. 

In fact, the wheat blast-resistant varieties produced by CIMMYT in collaboration with National Agricultural Research Systems partners have proven useful in reducing the impact of wheat blast.

Wheat blast-promoting conditions can also be avoided by choosing the appropriate sowing date. The adjustment in planting dates is another effective mitigation strategy against the disease, according to the researchers. 

Rain, followed by hot, humid weather during the flowering stage, can promote disease development. So, to reduce the risk of infection, the paper recommended avoiding early planting in central Brazil and late planting in Bangladesh, as these periods coincide with high temperatures and relative humidity due to increased precipitation levels.