Tuber melanosporum

Tuber melanosporum, called the black truffle, Périgord truffle or French black truffle, is a species of truffle native to Southern Europe. It is one of the most expensive edible fungi in the world. In 2013, the truffle cost between 1,000 and 2,000 euros per kilogram.

The round, dark brown fruiting bodies (ascocarps) have a black-brown skin with small pyramidal cusps. They have a strong, aromatic smell and normally reach a size of up to 10 centimetres (4 inches). Some may be significantly larger, such as a black truffle found in 2012 in Dordogne with a mass of 1.277 kilograms (2.82 pounds).

Their flesh is initially white, then dark. It is permeated by white veins, which turn brown with age. The spores are elliptical and measure about 22–55 μm by 20–35 μm. They are dark brown and covered with large spikes.

In the Northern Hemisphere, the fruiting bodies develop from April to June and are harvested from November to March.

Until 2010, all truffle species were thought to be homothallic, that is, capable of sexual reproduction from a single organism. Subsequent research indicated that black truffles are heterothallic; that is, sexual reproduction requires contact between the mycelia of different mating types. If mycelia of different mating types surround a tree, eventually, one type becomes predominant.

The fruiting bodies of the black truffle exude a scent reminiscent of undergrowth, strawberries, wet earth, or dried fruit with a hint of cocoa. Their taste, which fully develops after the truffles are heated, is slightly peppery and bitter. If stored at room temperature, the aromatic compounds dissipate, while storage around the freezing point (0 °C) leads to an increased synthesis of these compounds.

The volatile compounds that contribute to the aroma and are developed by the fruiting bodies include 2-methyl-1-butanol, isoamyl alcohol, 2-methylbutyraldehyde, and 3-methylbutyraldehyde, as well as traces of sulfur compounds. One of these, dimethyl sulfide, is what attracts truffle dogs, truffle hogs and truffle flies to the fruiting bodies. Several species of yeast, which produce part of the aromatic compounds, have been isolated from Tuber melanosporum and Tuber magnatum.

The genome of the black truffle was published in 2010. It contains 125 million base pairs, 58% of the genome consists of transposable elements, and the genome contains only 7,500 identified protein-encoding genes. During symbiosis, genes involved in the decomposition of plant cell walls and lipids are induced. This indicates that black truffles decompose the cell walls of their host plants at the beginning of the symbiosis.