High temperatures ‘make wheat old before its time’

Farmers in hot countries tend to sow wheat in cooler temperatures, when the crop thrives Copyright: Flickr/CIMMYT

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[SRINAGAR, INDIA] Global warming can cause premature ageing in wheat, according to computer modelling studies of the crop’s response to growing conditions in northern India.

The effects of warming on wheat growth and grain size are far worse than previous crop models indicated, David Lobell, assistant professor in environmental earth system science at Stanford University, United States, and colleagues wrote in Nature Climate Change last week (29 January).

Lobell’s team used nine years of satellite measurements of wheat growth in northern India’s Indo-Gangetic Plains to analyse rates of wheat ageing after exposure to temperatures higher than 34 degrees Celsius.  

Wheat thrives in relatively cool temperatures and therefore farmers across the world tend to sow the crop in late autumn or early winter, and harvest it before early summer — meaning that the grains form when temperatures are hottest.

But higher temperatures are known to reduce both the number of wheat grains and their size.

Now scientists have found that temperatures above 30 degrees Celsius affect the mechanism responsible for preparing food for the plant, which in turn causes early ageing and limits how much the grains can grow.  

The satellite data showed that variations in wheat yield in India could be attributed to these temperature effects. For example, a sudden rise in temperature in 2010 caused wheat plants to mature too early, reducing yields.

The researchers calculated that, if models took their findings into account, they would add an extra 50 per cent loss in wheat yields for each two degree rise at some times of the year.

"The effectiveness of adaptations will depend on how well they reduce crop sensitivity to very hot days," they wrote.

Whether the results would be replicated in other wheat-growing areas remains to be seen, they added.

Gulzar Singh, a senior scientist at the Sher-e-Kashmir University of Agricultural Science and Technology, Srinagar, told SciDev.Net: "The study certainly [highlights] the need to prepare for adaptations like developing heat-tolerant varieties".

Ravish Chatrath, principal scientist at the Directorate of Wheat Research, India, said that, although India has had a bumper wheat crop over the past five years, developing a mechanism to adapt to climate change is essential.

"We are constantly working to develop heat-tolerant [crop] varieties," he said.

Studies of the fates of individual crops under climate change have variously predicted both increases and decreases. An assessment was published in 2010 of how 50 key crops will fare in increasing temperatures.

Link to paper in Nature Climate Change


Nature Climate Change doi:10.1038/nclimate1356 (2012)