Tuber melanosporum: mating type distribution in a natural plantation and dynamics of strains of different mating types on the roots of nursery‐inoculated host plants

Abstract

Summary• In light of the recent finding that Tuber melanosporum, the ectomycorrhizal ascomycete that produces the most highly prized black truffles, is a heterothallic species, we monitored the spatial distribution of strains with opposite mating types (MAT) in a natural truffle ground and followed strain dynamics in artificially inoculated host plants grown under controlled conditions.• In a natural truffle ground, ectomycorrhizas (ECMs), soil samples and fruit bodies were sampled and genotyped to determine mating types. Simple sequence repeat (SSR) markers were also used to fingerprint ECMs and fruit bodies. The ECMs from nursery-inoculated host plants were analysed for mating type at 6 months and 19 months post-inoculation.• In open-field conditions, all ECMs from the same sampling site showed an identical mating type and an identical haploid genotype, based on SSR analysis. Interestingly, the gleba of fruit bodies always demonstrated the same genotype as the surrounding ECMs. Although root tips from nursery-grown plants initially developed ECMs of both mating types, a dominance of ECMs of the same MAT were found after several months.• The present study deepens our understanding of the vegetative and sexual propagation modes of T. melanosporum. These results are highly relevant for truffle cultivation.

Black Truffle, a Hermaphrodite with Forced Unisexual Behaviour

“…The first analyses confirmed that the genetic individuals forming the gleba were also present on surrounding mycorrhizae [6,7], establishing evidence for the trophic link between fruitbodies and tree roots by way of the maternal parent. Moreover, labelling of tree photosynthates by 13 [ 6 1 _ T D $ D I F F ] CO 2 successfully demonstrated the transfer of carbon from leaves to fruitbodies [8], supporting the nutritional role of maternal individuals.…”

“…The monitoring of trees in a nursery after inoculation by black truffle spores [6] suggested that although individuals with both mating types coexisted on young seedlings, one of the mating types was progressively excluded over time (Figure 2). The underlying mechanism is not yet fully understood, but a role for vegetative incompatibility has been suggested [6,10].…”

“…The underlying mechanism is not yet fully understood, but a role for vegetative incompatibility has been suggested [6,10]. Vegetative incompatibility is a common mechanism in fungi [11], where genetically close individuals reciprocally cooperate, mainly by hyphal fusion and resource sharing.…”

“…Paternal individuals only recently attracted detailed investigations [6,9,12]. Their genotype can be deduced from the zygotic genotype obtained by bulk extraction of spore DNA, by subtracting the maternal genotype as obtained by TIMI 1467 1-4 simple gleba DNA extraction (Figure 1).…”

Diversity, population genetics, and evolution of macrofungi associated with animals

“…In some populations, only one mating type can be found under a single host tree (Murat et al 2013) (Table 1). In other populations, Rubini et al (2011a), Zampieri et al (2012), and Linde and Selmes (2012) found biased distributions of two mating types of Tuber truffles under a single tree. Because sexual reproduction in Tuber species requires the mating between strains of two different mating types, the mycetophagous mammals play an important role for this to occur by bringing sexual partners into the proximity of root resident strains (Kataržytė and Kutorga 2011).…”