Reproductive biology of the black truffle Tuber melanosporum: contrasting ecologies of the two parents

The black truffle Tuber melanosporum is an ectomycorrhizal ascomycete of commercial value. Few is known about the reproductive biology of this famous edible mushroom. It is potentially hermaphroditic but reproduction – i.e. formation of the fruitbody (asco-carp) and production of meiotic spores (ascospores) within the later – requires mating between two individuals with opposite mating types. At fruiting, a maternal parent forms the ascocarp, whereas the paternal one only leaves genes in the ascospores. In addition, beyond ascocarps, maternal genotypes also form surrounding ectomycorrhizas, suggesting that they are established as tree symbiont. We summarize here novelties issuing from five years of sampling over France. In order to characterize the genetic structure of populations for both parents, we conducted gen-otyping analyses using 12 microsatellites to characterize maternal and paternal geno-types in ascocarps from seven truffle grounds. This revealed high inbreeding and a strong isolation by distance for maternal and paternal genotypes, ruling out the possibil-ity of gametic gene flow. Maternal individuals were bigger and more perennial than pa-ternal ones, more numerous and transient. Paternal genotypes were never found on sur-rounding ectomycorrhizas. This suggests that the two partners have different develop-ments and niches. We also investigated herbaceous plant roots as a potential niche for the two paternal partners by barcoding and, when possible, by genotyping T. melanosporum from these roots. Although the black truffle infects the herbaceous plants of truffle grounds, only maternal genotypes were again found here. We thus suggest that germinating asco-spores could act as paternal parent