Analysis: Scientists seek to solve ozone threat to Africa’s food security

ABERGWYNGREGYN, Wales, Aug 31 (Reuters) – Plant scientist Felicity Hayes checks her crops inside one of eight small domed greenhouses set against the Welsh hills. Potted pigeon pea and spring planted papaya are leafy and green, soon to bear fruit.

In a neighboring greenhouse, the same plants look sick and stunted. Pigeon pea is an old yellow with pale leaves; papaya trees only reach half the height.

The only difference between the two greenhouse atmospheres is ozone pollution.

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Hayes, who works at the UK Center for Ecology and Hydrology (UKCEH), is pumping ozone gas at varying concentrations into greenhouses where major African crops are grown. She is studying how increased ozone pollution could affect crop yields – and food security for subsistence farmers – in the developing world.

Ozone, a gas formed when sunlight and heat interact with fossil fuel emissions, can cause significant losses to farmers, research suggests, by rapidly aging crops before they reach full production potential and by reducing photosynthesis , the process by which plants turn sunlight into food.

Ozone stress also reduces plant defenses against pests.

A 2018 study in the journal Global Change Biology estimated that global grain losses from ozone pollution amounted to $24.2 billion annually from 2010 to 2012.

In a January article published in Nature Food, researchers calculated about $63 billion in losses in wheat, rice and corn annually over the past decade in East Asia. Read more

Scientists are particularly concerned about Africa, which will see more vehicle traffic and waste burning as the population doubles by mid-century.

This means more ozone pollution, a major challenge for smallholder farmers who make up 60% of the population in sub-Saharan Africa.

“There is serious concern that ozone pollution will affect yields in the long term,” said senior scientist Martin Moyo at the International Crops Research Institute for the Semi-Arid Tropics in Zimbabwe.

He stressed an “urgent need for more rural studies to determine ozone concentrations” across the continent.

Earlier this year, scientists with the UK-based non-profit Center for Agriculture and Biosciences International (CABI) set up ozone monitoring equipment around cocoa and maize fields in Ghana, Zambia and Kenya.

But most African countries do not have reliable or consistent air pollution monitors, according to a 2019 UNICEF report. Among those that do, few measure ozone.


In the stratosphere, ozone protects the Earth from the sun’s ultraviolet radiation. Closer to the planet’s surface, it can harm plants and animals, including humans.

While air quality regulations have helped reduce ozone levels in the United States and Europe, the trend is set to increase in the opposite direction for fast-growing Africa and parts of Asia.

Climate change could also speed things up.

In areas of Africa with high fossil fuel emissions and frequent burning of forests or grasslands, new research suggests that hotter temperatures may exacerbate the problem as they may speed up the chemical reactions that create ozone.

While research has found that North American wheat is generally less affected by ozone than its European and Asian counterparts, there has been less research on African versions of the same crops that over decades of cultivation have become better suited to those environments. .

Once every two weeks at a Nairobi market, rural farmers bring samples of their diseased crops to a “plant doctor” in the hope of determining what is affecting their yields.

“Many (ozone) symptoms can be confused with mites or fungal damage,” said CABI entomologist Lena Durocher-Granger. Farmers may continue to apply fertilizers or chemicals thinking it is a disease, but it is ozone pollution.

Her organization is working with UKCEH to help people identify the signs of ozone stress and recommend adjustments, such as watering less on high ozone days. Watering can leave the leaf pores wide open, allowing the plants to take in even more ozone.


In her greenhouses in Wales, Hayes was exposing crops in a dome to the lowest amount – 30 parts per billion – similar to the North Wales environment. In the dome with the highest ozone level, plants were getting more than three times that amount, mimicking the polluted conditions of North Africa.

Hayes and her colleagues have found that some African products are more affected than others.

In a dome filled with a medium amount of ozone, North African wheat plants had quickly turned from green to yellow in just a few months.

“You get small, thin grains that don’t have all the good parts in them, a lot of skin on the outside and not as much protein and nutritional value,” Hayes said.

This is consistent with research her team published last year on sub-Saharan plant cultivars, which found that ozone pollution can reduce sub-Saharan wheat yields by up to 13%.

Dry beans may fare worse, with estimated yield losses of up to 21% in some areas, according to the same study, published in Environmental Science and Pollution Research.

“Beans are a useful source of protein in Africa and farmers survive on a lot of them,” said Katrina.

Sharps, a spatial data analyst at UKCEH.

Sub-Saharan millet, however, appeared more ozone tolerant. However, Africa produced about half as much millet as wheat in 2020.

“If the soil and growing conditions are suitable,” Sharps said, “subsistence farmers may consider growing more millet.”

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Reporting by Gloria Dickie; Editing by Katy Daigle, Marguerita Choy and Bill Berkrot

Our Standards: The Thomson Reuters Trust Principles.

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