Subscribe
For the past seven years, Raizul Mondal and several other residents of Jalangi village in West Bengal’s Murshidabad district have been guarding India’s eastern borders. They have even sacrificed their livelihoods to prevent a catastrophe. Lurking across the international boundary in Bangladesh is an invisible enemy—Magnaporthe oryzae Triticum (MoT), a fungus that attacks wheat crops and can wipe out the entire harvest in a matter of days.
Before reaching Bangladesh in February 2016, the fungus had periodically ravaged 3 million hectares (ha) of wheat fields in South America since it was first identified in Brazil in 1985. An outbreak in 2009 had cost Brazil one-third of that year’s crop. The 2016 outbreak in Bangladesh—this is when the fungus made its first appearance in Asia—was equally rapid and devastating. Estimates by the country’s Department of Agricultural Extension show that the fungus caused wheat blast disease in 15,000 ha—3.4 per cent of the area under the crop in Bangladesh—reducing yield by 51 per cent in the affected fields. Since then, MoT has spread to 14 districts, including Jashore, Jhenaidah, Chadanga and Rajshahi that border India. By 2018, the fungus invaded Africa and wheat blast appeared in experimental plots and farms of Zambia. With its presence simultaneously on three continents, MoT has emerged as a global threat to food security. The fungus’ presence in South America could derail the efforts by Brazil and Argentina to tackle the global wheat supply shortage caused by Russia’s invasion of Ukraine, while its arrival in Zambia has put southern Africa’s wheat-producing countries at risk. In Asia, the Bangladesh outbreak is a grave concern as India and China are global leaders in wheat production.
Mondal and other residents of Jalangi, whose wheat fields hug the border fences, had their first likely encounter with MoT in February 2017. “The crops were ready for harvest, when the spikes suddenly lost their amber hue and appeared bleached,” Mondal recalls. Soon, complaints of similar symptoms started pouring in from other bordering villages in Nadia and Murshidabad districts. Baidul Islam, a farmer from Majhardiar village in Murshidabad, narrates the ferocity of the infection. “One evening I noticed that some spikes had turned silvery white. I returned to the field the next morning to spray fungicide, only to find that the disease had spread to one-third of the crop on my 3 bigha land (one bigha equals 0.25 ha). Even fungicides were ineffective and the entire crop shrivelled up and died in just five days,” says Islam.
The state’s agriculture department sprang into action and directed farmers in the villages, which had reported wheat-blast-like infection, to set fire to the standing crops to prevent the fungal spores from spreading further; 400 ha of wheat fields were reportedly set ablaze. Since the fungus can survive on seeds for up to 22 months, the government also announced a “wheat holiday” for three years in the state and banned cultivation of the crop within 5 km of the border with Bangladesh. The Border Security Force was also instructed to keep a vigil on grain trading.
The restrictions took a substantial toll on the farmers. Though rice is the dominant crop of West Bengal, farmers in the border areas grow wheat in the winter or rabi season. In fact, the nine border districts of West Bengal are major wheat-producing regions in the state. In 2015-16, Murshidabad accounted for 35 per cent—the maximum—of the wheat area of West Bengal. In March 2024, when Down To Earth (DTE) visited some of the border villages, there was a significant shift in the crop pattern. The number of people migrating to work as labourers, too, had increased. “The government had assured free ration to those who had to burn down their crops. But only a few households in my village received food grains,” says Mondal, who worked as a daily-wage labourer for a year to provide for his family. Officials with the agriculture department tell DTE that in most villages the ban was lifted in 2022. Gyanendra Singh, former director of the Indian Institute of Wheat and Barley Research, Karnal, says, “India has developed over two dozen wheat-blast-resistant varieties along with the International Maize and Wheat Improvement Center (CIMMYT), Mexico. These varieties are now being provided to farmers in West Bengal’s border villages.”
But Mondal has no plans of growing wheat. He has set aside half of his 6 bigha land for banana plantation and grows jute, maize and lentils on the remaining land.
In Majhardiar village, Islam and his brother had left for Kerala to work in a garment factory shortly after the ban was announced. Since the village has farms straddling the border fence, the government extended the ban in Majhardiar by another year. In 2023, as soon as wheat seeds became available in the market, Islam returned home. He and several other farmers in the village sowed wheat, but lost the crop to wheat blast-like symptoms. Islam now plans to migrate again.
So far, India has managed to thwart the fungus—at least, so it seems. But scientists warn that this may not last long. According to CIMMYT, MoT has an affinity for warm and humid weather. Its spore production increases if temperatures are between 15oC and 27oC and humidity is above 93 per cent. Foggy weather or rainfall then cause the spores to fall onto leaves or heads, causing blast infection. Usually, the timing of infection coincides with the reproductive stage of the crop, causing widespread losses.
Researchers from CIMMYT and other institutes in Germany, Bangladesh, Brazil and the US have modelled how wheat blast would spread under the changing climate that is characterised by both warmer and more humid conditions. They have found that the fungal disease could reduce global wheat production by 13 per cent by 2050. In their study paper published in the journal Nature Climate Change on February 1, 2024, the researchers predict that the disease would spread primarily in tropical regions, with substantial potential yield losses in South America, South Africa and South Asia—the major wheat-growing areas. The fungus would also penetrate countries that were previously untouched, and these include, Uruguay, central America, southeastern US, East Africa, India, eastern Australia. Climate in European regions closer to the Mediterranean may become conducive for the disease to spread, putting Italy, France and Spain at risk.
What’s alarming is that areas affected by wheat blast are also among those severely impacted by climate change, and where food security is already a challenge. For instance, wheat production in Zambia is rain-fed, grown primarily by small-scale and resource-poor farmers, who typically attain low yields. DTE visited Mpika district of Muchinga province, which reported wheat blast outbreak in 2018. Gertude Chonya, a small farmer from Mufubishi locality, tells DTE that the loss of wheat has directly impacted food availability and income. “We did not have flour for breakfast in the outbreak year and had to depend on nshima (porridge made from maize). Our income diminished as we could not sell wheat or make wheat fritters for sale,” says Chonya.
As of now, no commercially available wheat variety offers complete resistance to wheat blast. A few varieties offer only moderate resistance. Since farmers rely heavily on fungicides to manage the disease, MoT is increasingly becoming resistant to those widely available arsenal. Paul Nicholson, professor at John Innes Centre, UK, a centre for research in plant and microbial science, explains what makes the fungus so invincible. “Diseases in wheat have been known to be around for thousands of years. Examples go back to Biblical times. But wheat blast is new and little is known about it,” Nicholson says. Besides, MoT fungus is physiologically and genetically complex. So even after three decades, scientists do not fully understand how it interacts with wheat or which genes in wheat confer durable resistance to it.
According to CIMMYT, the blast grows well on several other plants and crops. So growing wheat on a rotational basis does not confer protection to the crop. Since the fungus also hitchhikes on seeds and crop residues, good management practices, such as screening seeds, certifying them for the fungus and quarantine measures, can help thwart its spread to other countries. But this is clearly not happening. Scientists have identified that the outbreak in Bangladesh followed a series of wheat shipments from South America. A similar route is responsible for the outbreak in Zambia.
Researchers worry that as the fungus spreads to wider geographies, it may evolve to become more virulent or infect other species. Pawan Kumar Singh, a senior scientist who heads wheat pathology group at CIMMYT, says, “There is no information yet on the Triticum pathotype jumping hosts in large scale in field conditions. But the consequences can be devastating if the disease undergoes cross-infection and spreads between two crops. The chances cannot be ignored as the pathotype evolves fast, leading to higher genetic diversity than its counterparts.”
It could already be evolving. According to a July 2021 review article published in Frontiers in Plant Science, between 2017 and 2021, weather conditions in Bangladesh during the wheat growing season were cooler and drier and did not favour blast infection and spread. Still, the disease did not remain confined to the initial eight affected districts but spread to 14 new districts. Does this mean a plant pandemic is in the making? Read on.