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Heat-loving citrus fruits

Ulrike Gebhardt/ssJuly 2, 2013

Citrus fruits are packed with important nutrients and minerals. And that’s not the only great thing about the fruits. They’re also proving to be experts at adapting to climate change - much better than other plants.

Yellow and green citrus fruits (Foto: Shaun Dunphy / CC BY-SA 2.0)
verschiedene ZitrusfrüchteImage: Shaun Dunphy / CC BY-SA 2.0

Oranges, grapefruits and lemons – they often cover great distances until they land on supermarket shelves. The bright, juicy produce might look fresh and healthy, but the fruits aren’t as robust as they seem.

Soon after being harvested, citrus fruits can very easily develop a film of mold along the outer skin. To prevent that from happening, producers spray the fruit with a wax solution that keeps it from drying out and creates a shiny exterior. But the spray also contains a fungicide called Thiabendazole – a slightly toxic substance that should be avoided, along with the fruit peel in general.

But beyond the peel, citrus fruits are real superfoods. They contain high levels of vitamins C, B1 and E. In fact, a quarter of a liter of orange juice alone provides the daily required amount of vitamin C. In the 18th century, lemon juice was distributed on board British marine ships to prevent the outbreak of scurvy, a disease that stems from vitamin deficiency.

Two men on a beach sell juice at a stand covered in oranges(Foto: Adam Jones / CC BY-SA 2.0)
Oranges and other citrus fruits provide important nutrientsImage: Adam Jones / CC BY-SA 2.0

Citrus fruits also offer important nutrients like folic acid, potassium, selenium, carotenoids and flavonoids, which help strengthen blood vessels and prevent strokes, studies show. The vitamins and minerals in citrus fruits also help fight type 2 diabetes that is often linked to obesity.

The lemon belt exporters

With their refreshing mix of sweet and sour taste, citrus fruits are beloved the world over. The longer they stay on the branch and in the sun, the sweeter they become. But once they’re picked, they stop ripening and producing sugar, so producers have to be careful not to pick their harvest too soon.

There are some 140 countries that produce citrus fruits, most of which lie along what’s been dubbed the “citrus belt” - a subtropical region near the equator. The fruit harvests are then shipped across the world, generating a volume of trade that eclipses the export of peaches, pears, cherries or even apples.

It’s believed that citrus fruits are native to Southeast Asia, India and China and were first introduced to Europe – in Greece and Turkey - by Alexander the Great’s armies in the 4th century. Christopher Columbus carried citrus seeds with him to the Caribbean island of Hispaniola.

An image of an orange tree (Foto: U.S. Department of Agriculture / CC BY 2.0)
The so-called citrus belt lies along the equator and produces most of the world’s citrus fruitsImage: Shaun Dunphy / CC BY-SA 2.0

And in 1654, the first lemon and orange bushes found their way from Saint Helena Island in North America to South Africa, which today is the second largest exporter of citrus fruits after Spain. In 2010, South Africa shipped 140,000 tons of lemons and limes to mostly Asia and Europe.

Great Britain has always been a big consumer of South Africa’s citrus products. In 1902, British author Rudyard Kipling – known for penning The Jungle Book – described the arrival of “very tasty” South African fruits in England, where the climate makes the cultivation of such produce impossible. Lemon bushes are, for example, extremely sensitive to cold and are best grown in subtropical climates.

Climate change: pros and cons for citrus

But citrus fruit plants are still considered to be better equipped to deal with a changing climate than other crops and plants. That’s largely because they flourish in the heat.

According to a 2007 study that examined the effect of rising temperatures on various crops, the cultivation area for orange trees will actually expand by the year 2055. While the lemon cultivation area will shrink by around 10 percent, that is a small setback in comparison to other plants. Strawberry producers, for example, will lose around 32 percent of their arable land, and wheat fields will be eroded by around 18 percent, according to the study.

“For the lemon harvest, we’re not expecting any major drawbacks due to climate change for the time being,” according to Tim Grout from Citrus Research International, a research association that examines the citrus industry in southern Africa. “If however temperatures rise by more than one or two degrees, yields could fall because the plants shed their fruit too soon,” he says, adding that seedless lemons are especially at risk.

Citrus greening has disfigured the seeds and flesh of this tangerine (Foto: J.M. Bové / Bugwood.org / CC BY-NC 3.0 US) ++ J.M. Bové / Bugwood.org / CC BY-NC 3.0 US ++
Citrus greening causes a plant’s fruit to turn green and bitterImage: J.M. Bové / Bugwood.org / CC BY-NC 3.0 US

Other analysts believe that the increased risk of pest infestations could also lead to greater harvest losses. Citrus greening, for example, is a bacterial disease that is primarily spread by two types of psyllid insects. It turns a citrus plant’s leaves and shoots yellow and makes the fruit bitter, often causing the entire plant to wither away.

Lemon growers in South Africa might see their yields shrink due to climate change, but Tim Grout says those losses won’t be noticeable on a national scale. Lemon cultivation is divided among three climate zones in South Africa: from the low-lying, tropical region in the northeast of the country (which includes Limpopo and KwaZulu-Natal provinces) to the higher subtropical areas and the cooler provinces of Eastern and Western Cape.

South Africa’s diverse climate a boon

“If it’s too hot for the lemons in Limpopo, you can increase production in the Eastern Cape area, where most of the lemon trees already grow,” Tim Grout says.

The country’s diverse range of climates also allows growers in South Africa to harvest across several seasons and produce various types of citrus fruits according to the local temperatures. Grapefruits and tangerines, for example, grow best in the northern regions while oranges flourish in the south.

In other countries where that variety of climate doesn’t exist, growers are searching for resilient fruits and vegetables that are resistant to heat and dry weather. And there are a few setbacks. Although time and money is needed to improve plant cultivation, investment in plant breeding has fallen in 19 African countries, according to the Rome-based research organization Biodiversity International.

That's bad news for citrus fruit lovers. That’s because it takes a few years for growers to breed new plant types that can survive changing climatic conditions.