Efficiency of the traditional practice of traps to stimulate black truffle production, and its ecological mechanisms.

The black truffle Tuber melanosporum was disseminated all over the world, propelled by the development of a wide variety of empirical practices. A widespread practice, called 'truffle trap', consists of placing pieces of truffles into excavations dug under host trees, and of collecting truffle in these traps in the next years. This research aims at (1) evaluating the effect of this practice on fruitbody production based on the analysis of 9924 truffle traps installed in 11 orchards across T. melanosporum native area in France and (2) exploring the mechanisms involved in fruitbody emergence using traps where the genotypes of introduced truffles were compared with those of fruitbodies collected in the same traps. We confirmed that truffle traps provide a major and highly variable part of truffle ground production, representing up to 89% of the collected fruitbodies. We evidenced a genetic link between introduced spores and collected fruitbodies, and then demonstrated that truffle growers provide paternal partners for mating with local maternal mycelia. We also highlighted that soil disturbance stimulate the vegetative development of established maternal mycelia. This research supports that a widely used traditional practice enhances fruitbody production by shaping favorable conditions and providing sexual partners required for fruiting.

Population genetics and dynamics of the black truffle in a man-made truffle field.

The colonization dynamics of the black truffle in an artificial field were assessed through analyses of microsatellite and RAPD markers. The truffle field was composed of three tree species and mycelial inoculum of three different origins, and was monitored for the first three years of truffle production. We found very low levels of genetic diversity. Isolation by distance was detected only at the between-tree level. This could be interpreted as local colonization around each tree facilitated by the presence of the tree root system. At the larger spatial scale of the European range, the absence of isolation by distance corroborates the hypothesis of an impact of glaciation on genetic variation, followed by rapid postglaciation demographic expansion. In addition, genetic variation of harvested truffles was explained by neither inoculation origin, nor tree species. Our study questions the real impact of man-made inoculation of tree root systems with fungal mycelia.