Soil spore bank in Tuber melanosporum: up to 42% of fruitbodies remain unremoved in managed truffle grounds.

Fungi fruiting hypogeously are believed to form spore banks in soil especially because some fruitbodies are not removed by animals. However, little is known on the proportion of fruitbodies that are not removed by animals. We took advantage of the brûlé phenomenon, which allows delineation of the mycelium distribution, to assess the proportion of unremoved black truffle (Tuber melanosporum) fruitbodies in the context of plantations where fruitbodies are actively sought and harvested by truffle growers. We inspected portions of the brûlés after the harvest season to find unremoved fruitbodies. On average, from six truffle grounds in which a total of 38 brûlés were investigated, unremoved fruitbodies represented 33% of the whole fruitbody production (42% when averaging all the brûlés). We discuss this value and its high variability among truffle grounds. Beyond the local and variable accidental reasons that may lead to this high proportion, we speculate that the formation of some undetectable fruitbodies may be under selection pressure, given the reproductive biology of T. melanosporum.