Summary: Truffle fungi grow on the roots of plants in a mutually beneficial association known as a “symbiosis”, where the fungus receives food from its plant partner and gives soil nutrients in return. It is this close association with plants that enables truffles to reproduce, giving rise to precious fungal bulbs with enticing flavors.
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Plants are able to use sunlight, water, and carbon dioxide to produce their own food through “photosynthesis”. By contrast, fungi are incapable of generating their own food and have developed various strategies to nourish themselves. One of these strategies is symbiosis which consists in living together with a plant partner to obtain food.
Truffles enter in symbiosis with plants in a very specific manner. Like any other fungi, truffles are able to grow in the soil as thin filaments known as “mycelium”. Truffle mycelium can swirl around plant roots, creating a knuckle-like structure which is a mixed-organ, half-fungus, and half-plant, and which is the basis of the symbiosis.
The mixed organ functions as a trading platform between the two partners. On one hand, truffles receive food from their plant partner under the form of sugars. On the other hand, the fungus supplies nutrients to the plant by growing thin filaments deep into the soil and harvesting minerals.
But how do truffles, the precious edible fungal bulbs, actually form?
The globular fruits of truffles, otherwise known as fruiting bodies, are formed following sexual reproduction between two truffles of opposite sexes that grow as filaments. This was first understood in 2001 after deciphering the genetic code (the genome) of a black truffle that is widely distributed in Spain, France, and Italy.
What happens in practice during reproduction is not fully understood though. The current model suggests that truffle filaments colonizing plant roots enter in contact with a truffle filament of the opposite sex. This encounter might lead to reproduction and the birth of a tiny baby truffle that has merely the size of a green pea.
Once the baby truffle is born, it still receives food from its plant partner, which enables it to grow in size. How much time is exactly needed for the truffle to reach a typical adult size of a few centimeters is unknown, but this might take weeks or months, and might be influenced by various factors (i.e. climate, the specific truffle sort, etc.).
Truffles do not colonize any plants and have marked preferences
Among the numerous fungi that associate with plants in nature, some are very promiscuous, and others a much pickier and prefer a few specific plant partners. Actually, the vast majority of plants (approx. 90%) are colonized by fungi, and so are trees in a forest and garden plants as well.
Truffles only make associations with a handful of plants, which are predominantly trees. The plant sort depends on geographical location as the tree must be adapted to local climatic conditions. For instance, the European truffle sorts typically grown on the roots of oak, hazel, and beech but in Texas, the “pecan truffle” prefers pecan trees.
The fact that truffles need to partner with plants in nature was understood in 1914. Methods to produce plants with truffle filaments on their roots were quickly developed thereafter and such seedlings can be used today to establish truffle orchards. Truffle yield is however uncertain (read more here about truffle plantations & wild orchards).
Why is this relevant?
A better understanding of the biology of truffles and more specifically their life cycle/reproduction could have economic but also ecological implications. On one side, this might lead to a steadier supply of truffles, which is believed to have declined by almost 90% over the last 100 years. It could also lead to better forest management practices since symbiotic fungi boost plant immunity and resistance to water stress.
Written by Richard Splivallo
Richard is the CEO of Nectariss and a truffle expert. As a former university professor, he has dedicated almost 20 years of his life to better understand the complex biology of truffle fungi and has authored more than 25 scientific publications on that topic.