How climate change could kill the red apple

The archetypal apple is – no two ways about it – red. There may be yellow apples or green apples in the grocery store too. In some places, you might even find varieties that are striped or mottled with a profusion of hues, like the gorgeous Cox’s Orange Pippin.

But red – or occasionally, pure, sharp Granny Smith green – is the colour of apples in most alphabet books. It’s an interesting detail, because apples were not always so resolutely monochrome.

The ancestors of the modern apple were wild trees growing in what is now Kazakhstan, on the western slope of the mountains which  border western China. Today, wild apple trees still grow there, perfuming the air with fallen fruit and feeding the bears that lumber through the forest, although the wild apples’ numbers have shrunk by 90% in the last 50 years thanks to human development and their future is uncertain.

The fruits range from pale yellow to cherry red and spring green, but red is not generally more prominent than the other colours. (One apple-loving traveller, Beck Lowe, reports that ironically a commercial Kazakh orchard, like orchards everywhere around the world, is growing Red Delicious and Golden Delicious, apples of American origin.)

Apple colour arises from the expression level of certain genes in the skin, scientists have found. David Chagne, a geneticist at Plant and Food Research in New Zealand, explains that sets of enzymes work together to turn certain molecules into pigments called anthocyanins, the same class of substances that give purple sweet potatoes, grapes and plums their colour.

The levels of these enzymes are controlled by a transcription factor – a protein that regulates how much a gene is expressed – called MYB10, such that the more MYB10 there is, the redder the skin will generally be. In fact, one study found that in apples with red stripes, MYB10 levels were higher in the striped portions of the skin.

Red to green apples (Credit: Getty Images)

As temperatures rise, chemical changes within the apple make a red skin less likely (Credit: Getty Images)

Intriguingly, colour also depends on temperature. To get an apple that’s fully red, temperatures must stay cool, Chagne says, because if they climb to above about 40C (104F), MYB10 and anthocyanin levels crash. In the Pyrenees region of Spain, he and his colleagues found normally vividly red striped apples were completely pale after a particularly hot July. As temperatures warm, he suggests, it could become more difficult for apples to turn red.

He and colleagues are nonetheless looking to breed red-as-red-can-be fruits for the Asian market, where a deep ruby is a popular colour, using their understanding of the biology behind colour.

Perhaps the threat that climate change poses to the red apple will be counterbalanced by our sheer determination to breed them, even if it takes expensive breeding programmes. Even before we understood the genetics, colourful apples exerted a strong pull on humans. John Bunker, an apple collector based in Palermo, Maine, has rescued numerous forgotten breeds from extinction. These include apples that used to be grown a century or more ago before orcharding became so Delicious-focused, including the magnificent Black Oxford, an apple whose red is so dark you might mistake it for an enormous plum before seeing its brilliant white flesh. “The colours are phenomenal. And I think that for some people including myself that was the original attraction,” he says.

In a culture of small diversified farms and small diversified farm economies, uniformity is of limited value – John Bunker

Colour probably didn’t trump other features of an apple when growers were evaluating a new tree, however. Instead, they focused on the taste and use for the apple: some are good for cider, some for pies, some for sauce, and some for eating. It didn’t much matter exactly what the fruit looked like and whether it looked the same from tree to tree, because farmers were growing fruit for themselves and for their local market, and function mattered more than looks.

Bunker says that all changed about a hundred years ago. “In a culture of small diversified farms and small diversified farm economies, uniformity is of limited value,” he says. But if apples grown for thousands of miles around are [to] be bought as interchangeable, the colour becomes a kind of branding. It says “this is what to expect”. In this commodity system, uniformity was growing more valuable. At the same time, apples began to be picked before they were truly ripe so they could be shipped long distances without rotting.

There was a problem, however. “Colour is a ripeness indicator,” Bunker points out. Apples picked early didn’t have the right colour. But then an apple with a mutation that gave it a rich red tone before it was ripe came to the fore, he explains. That apple was eventually dubbed the Red Delicious, and in 1921 was released commercially for orchardists.

Countryside near Almaty, Kazakhstan (Credit: Getty Images)

The ancestors of the many differing apple varierties we enjoy today come from the countryside of Kazakhstan (Credit: Getty Images)

Other apples rose in the ranks as well – varieties that were discovered to have a regular, uniform colour, especially if it came before the apple had actually reached full ripeness, were good for business.

The number of varieties farmers grew started to shrink. And little by little, some of these varieties stopped tasting so good, as the emphasis on appearance didn’t encourage growing for flavour. David Bedford, an apple breeder at University of Minnesota, says that he grew up eating Red Delicious and consequently not being very fond of apples: it took him trying another variety in college to awaken him to the possibility that apples could be different, he reflects, “not skin like Naugahyde and texture like Elmer’s glue”.

He and his colleagues are behind the wildly successful Honeycrisp apple, released some years ago and known for its juicy crispness. And in fact, the Honeycrisp they released was a yellow-and-red-striped beauty.

Ever since man has been making choices they’ve been making them redder and redder – Dave Bedford

But even in apples bred to get away from the curse of the Red Delicious, the inexorable drive for red continues. People have now introduced Honeycrisps with mutations that make them more and more red. “It happens to every single apple on the market,” says Bedford. “That’s just the nature of our desire to have apples the way we want to them to look… ever since man has been making choices they’ve been making them redder and redder.”

The redder apples might not be better than the yellower ones – in fact they might be worse – but, he explains that “red sells, that’s the problem”. To attempt to correct for this in future apples, the University of Minnesota has released other apples under what’s called a club model. In this system, growers aren’t allowed to select for redder fruit.

When you see the wild variety of colours that is possible, and recognise the danger of an ever-redder drift disconnected from true flavour, it can make you hope for better days to come for apple eaters. Will the apple’s true, weird nature ever triumph over the hunt for red? History suggests it will be an uphill battle, but we can all dream.

Source: BBC