Subscribe
A plant pandemic could provoke a humanitarian crisis—a crisis that could deprive people of livelihood and lead to widespread hunger. The world has witnessed such crises in the past. Between 1845 and 1852, Phytophthora infestans wiped out potato crops in Ireland, resulting in the Great Famine and mass migration. The UK government estimates that 1 million people were affected either by disease or hunger. Similarly, during the 1943 Bengal famine, Cochliobolus miyabeanus that causes brown spot disease in rice led to the death of over 2 million people. In recent years, 400,000 coffee workers in central America lost their livelihood and had to migrate after coffee leaf rust disease infected plantations, states a 2021 study published in Agricultural Sciences. “The war between Russia and Ukraine has shown us how vulnerable we are to perturbations in the global supply of wheat and how shortages can lead to rapid increases in price affecting trade,” warns Paul Nicholson, professor at the John Innes Centre in the UK.
However, averting the crisis seems difficult at a time when the food industry is in the pursuit of high-performing cultivars and industrial productivity. This has bereft the crops of genetic diversity that confers them resistance against pathogens. Consider banana. There are over 1,000 edible varieties of bananas, some of which are far sweeter and nutritious than the Cavendish variety. But the quest of the industry to grow uniformly yellow bananas has resulted in plantations that are filled with genetically identical clones, produced from one mother plant in laboratories. In the absence of genetic diversity, these plantations get simultaneously wiped out in case of an infestation. This trait of banana failed Gros Michel and is now acting against Cavendish.
Similarly, soybean and wheat are extensively grown in high-density monocultures, and their yields are compromised by a plethora of pests and pathogens. Soybean rust caused by the fungus Phakopsora pachyrhizi and wheat blotch caused by the fungus Zymoseptoria tritici are among the most destructive diseases on these crops, and yield losses of more than 50 per cent have been documented during severe epidemics, according to a review article published in Nature Reviews Microbiology in May 2023.
An overhaul of the way we grow food is pertinent because plant pathogen loads and disease pressure are likely to change under future climate scenarios. Nick Talbot of The Sainsbury Laboratory, UK, says extreme weather events such as tropical storms have shown potential to spread diseases. Wheat blast outbreaks in Bangladesh, for example, have often followed tropical storms and heavy rains. A May 2021 study, “The persistent threat of emerging plant disease pandemics to global food security”, published in Agricultural Sciences, notes that extreme weather events like hurricanes can transport pathogen spores over continents. It says Hurricane Ivan in 2004 caused soybean rust movement from Brazil to the US.
Another research, published in Scientific Reports in April 2024, concludes that a rise in global warming from 1.5°C to 4°C is expected to increase the risk of Pierce’s disease (a bacterial disease that affects grapevines) epidemics in vineyards of southern Europe, particularly in France, Italy and Portugal. A 3°C increase indicates expansion of disease to the Mediterranean region and beyond. In a warming climate, wheat blast will spread to countries that so far remain untouched.
To aggravate the matter, elevated temperatures can suppress plant immunity, leading to increased pathogen infection, states the article in Nature Reviews Microbiology. For example, prolonged drought causes water stress in plants, which results in increased susceptibility to infection by pathogens. Climate change can also facilitate the emergence of new strains of pathogens, which in turn can break down resistance of the host plant, notes the article. Elevated carbon dioxide levels in the atmosphere are also seen to increase the severity of certain pathogens like powdery mildew that infects gourds.
Mitigating the future risks also requires effective monitoring and management of plant diseases. Scientists suggest taking a leaf out of the COVID-19 pandemic, by using genomic surveillance to help control the spread of diseases. For example, researchers have recently conducted a genomic surveillance of wheat blast fungus. In a 2023 study, published in PLOS Biology, they note that the technique enables rapid and accurate pathogen identification and allows tracing of the outbreak origin, which can direct preventive measures. Scientists from Bangladesh used a similar disease surveillance and monitoring mechanism, OpenWheatBlast, to share genomic data and analysis related to wheat blast and could track down its origin to South America.
The International Maize and Wheat Improvement Center (CIMMYT), Mexico, has also formed a Wheat Disease Early Warning Advisory System (Wheat DEWAS), which has introduced new analytic and knowledge systems capacity to one of the world’s largest and most advanced crop pathogen surveillance systems. The project allows researchers to build an open and scalable system to prevent disease outbreaks from novel pathogen strains threatening wheat productivity and food security in South Asia and East Africa. Talbot says scientists in Japan, UK, and other countries are working on surveillance of the spread of wheat blast disease and identifying potential mutations. “There are about a handful of strains identified by scientists that work against the wheat blast. The Rmg8 gene developed is the strongest thus far. But more efforts are needed to identify resistance genes and add multiple protection layers to the crop to safeguard against wheat blast,” he adds.
Coordinated effort and active surveillance are the only ways to beat pathogens in this warming and globalised world.