Climate Change

Extreme heat, drought make crops more vulnerable to soil-borne diseases: Study

Plant-eating fungus in the soil flourished at high temperatures, researchers found

By Pushp Bajaj
Published: Tuesday 04 February 2020

High temperatures and drought-like conditions caused the pathogenic fungus Pythium ultimum to flourish in soils, in turn leading to death of agricultural crop seedlings, a recent study found.

The research added to growing scientific evidence that climate change is severely affecting agricultural productivity around the world. With rising extreme weather events, heat and water stress and poor adaptation policies, the effects will only get worse in the future.  

The findings were published in the international journal of Applied Soil Ecology last week.

An international team of scientists used soils from different climatic locations in Europe to assess the resistance ability of different soil types. Samples were collected from cool and damp Scotland, temperate northeast Germany and dry and warm eastern Hungary. 

Agricultural productivity was then tested by sowing peas in these soils under extreme heat (40 degrees Celsius) and low water (only half soil moisture) availability, resembling drought-like conditions, in climate-controlled chambers. 

Hardly any of the pea plants survived the climate stress, the experiments showed. Those that did, withered under the fungal attack.

Typically, soils contain microorganisms that act as shields for the plants and protect them against the fungus. However, the added stress from high temperatures reduced the ability of these microorganisms to protect the plants. 

This made the already aggressive Pythium ultimum even more pervasive.

Once infected by the fungus, the pea plants developed root rot and died. “In some cases, there was a total failure of the germinating seedlings,” Christian Burns, researcher at the Section of Organic Farming and Cropping Systems at the University of Kassel, Germany, said in a press release

The effects were most dramatic for the cool, damp soils of Scotland that are less adapted to heat and drought stress. Hungarian soils that are frequently exposed to such conditions in summer were found to be more resistant. 

The researchers further investigated whether soils (and the protective organisms) can recover from the temperature and water stress if allowed enough time. This was done by delaying the introduction of the harmful fungus and the sowing of peas by several weeks after treating the soils with heat and drought stress.  

While soil samples from Scotland showed some signs of recovery, the time delay seemed to make fungal attacks worse for the soil from Hungary. This indicates that soils that are otherwise highly resistant to drought and heat stress, do not seem to recover quickly from extreme conditions. 

“Heat and drought have a negative impact on the soil organisms protecting plants from diseases,” said Thomas Döring, professor from the Agroecology and Oceanic Farming Group at the University of Bonn in Germany, in the press statement. “This increased the plants’ susceptibility to soil-borne pathogens,” Burns added. 

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