Soil pathogens rise as temperatures do

Pathogenic plant fungi are likely to multiply and spread as rising temperatures warm soils, thereby accelerating climate change-induced crop losses, according to research published in the journal Nature Climate Change.

Global food security is under threat as warmer temperatures increase populations of pests such as the virulent oomycete Phytophthora infestans, which was responsible for the Irish potato famine and is still causing problems.

“Soil-borne plant pathogens already cause hundreds of billions of dollars in crop losses each year,” says co-author Brajesh Singh from Western Sydney University, Australia.

“Our study suggests that common plant pathogens such as Fusarium and Alternaria species will become more prevalent under projected global warming scenarios, which will add to the challenges of maintaining world food production alongside other climate change-driven crises and a burgeoning human population.”

Soil-borne fungi such as Alternaria alternata, Fusarium oxysporum and Venturia inaequalis are some of the most devastating plant pathogens, against which chemical fungicides are virtually useless. 

But while information on plant diseases is growing, mapping out their current and future global prevalence would shed more light on the problem.

The research team, drawn from Europe, Australia and China, used a field survey across 235 natural ecosystems from six continents that ranged from forests and croplands to deserts, capturing 73% of environmental conditions on the planet. 

Combining this with a nine-year study investigating the impact of temperature on the prevalence of soil-borne fungi, they created a global map for the pathogens’ current and global distribution under different climate change scenarios.

The analysis included modern DNA sequencing techniques to establish the response of plant pathogens to warmer conditions.

Results showed that Venturia is widespread across the globe, and Fusarium, Phoma and Alternaria are most prolific in warm areas such as dryland and tropic ecosystems.

But with global warming, the pathogens are projected to thrive in most regions across the world irrespective of the climate and land use, with increased temperatures of two degrees Celsius nearly tripling their relative prevalence. 

Alternaria was the most common genus, for which the relative increase would be sevenfold and its total growth twofold. The relative abundance of Fusarium, another globally dominant fungus, could increase fivefold and Cladosporium spp 20-fold.

Areas likely to be hit the hardest by warming are soils across the Northern Hemisphere, towards the Arctic, and in South Africa.

The authors note that their results are global and don’t drill down into local, fine scale impacts, nor factor in pathogen infection, host disease or differences between ecosystems.

But the study does help pinpoint areas that are likely to feel the greatest impacts on food security first.

“Combining multiple layers of data offers a very powerful means for pinpointing priority regions,” says Singh.

It also underscores the importance of fast-tracking sustainable agricultural practices.

“We can advocate for strategies that promote plant and human health, build healthy soils and use non-chemical methods to win the battle between crops and pathogenic fungi.”