For truffle aroma, it’s not all about location

Genes, not environment, play a key role in the prized fungus' scent

Mon Dieu! A truffle’s delectable aroma may be as much about genetics as it is about geography.

The aromatic signature of the Burgundy truffle is best explained by genetics, not the local environment. Richard Splivallo

For years a truffle’s flavor has been mostly attributed to environmental factors, akin to how terroir — the soil, climate and geology of a region — bestows qualities to wine. But a new analysis, published online March 6 in New Phytologist, finds that a truffle’s particular blend of chemical compounds is linked instead to its genetic background.

By casting light on what gives these elusive underground fungi their prized flavor, the study could help transform several truffle species from wild harvest to consistent crop.

“Truffles are a really valuable natural resource, and it’s the aroma that really gives them their value,” says Gregory Bonito, an expert in truffle evolution at Duke University.

But teasing out what gives a truffle its aromatic oomph has been tough, thanks in part to the complexity of the truffle lifestyle. Truffles are the fruiting body of a particular group of fungi. These fungi strike up partnerships with various tree species, so that the fungal spores germinate and grow into threadlike structures on the trees’ roots. When fungal threads of different mating types find one another in the soil, sexual reproduction occurs and small truffles develop. Months later, pigs — or, increasingly, dogs — sniff out the truffles, which are buried 10 to 30 centimeters deep. The gastronomic delicacies are dug up, and the most prized species may sell for thousands of dollars per pound.

Some enthusiasts attribute a truffle’s aroma to its patch of soil, or whether spring was wet enough or winter cold enough. Another factor may be the tree species colonized, which include firs, oaks, hazels, pecans and pines. And truffles themselves are colonized by microbes that are also thought to contribute to the warty lumps’ flavor.

Particular genetic strains of yeasts used in making wine are known to influence quality and flavor, and bacterial strains may influence the flavor of cheeses, says Richard Splivallo of the University of Goettingen in Germany, who led the new work. But while the genetic blueprint for the famed black Périgord truffle (Tuber melanosporum) was published in 2010, the genetic particulars of other truffle species aren’t well understood. “We wanted to add the genetic dimension into the picture,” Splivallo says.

So the researchers collected more than 200 Burgundy truffles from seven countries over four years. Unlike the famed black truffle that grows mainly in France, Italy and Spain, the Burgundy truffle (known as both Tuber uncinatum and Tuber aestivum, until scientists realized they were the same species) is found throughout Europe. The scientists examined the profile of volatile chemical compounds that contribute to the truffle’s delicate, nutty flavor. A truffle’s scent comprises 20 to 50 volatiles, which act as cues for spore-dispersing insects and mammals and may regulate interactions with other plant roots and soil microorganisms.

In some instances, truffles growing in the same patch of land had different concentrations of these volatiles, the researchers found. And when they grouped the truffles by their genetic relatedness, truffles that were more closely related had more similar volatile profiles than more distantly related truffles.

“This is the first study to show a clear link between volatiles and genetics,” says Claude Murat, who studies truffle genetics at the French National Institute for Agricultural Research in Nancy.

The research might bring Burgundy truffles a step closer to being farmed, he adds. They are currently harvested primarily from the wild.

The discovery that genetics plays a role in imparting the flavor to Burgundy truffles may seem intuitive. After all, whether an apple makes good eating doesn’t depend only on where it grew and when it was picked — the apple’s genes matter too.

But the understanding of truffle life history and genetics is years behind domesticated fruit crops.  “It’s like we’re back in the Stone Age,” Bonito says. “We can culture them in the lab, but we don’t know how to make them fruit. Sex happens below ground in the dark. We still have a long way to go.”

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