Genetic Diversity and Mating Type Distribution of Tuber melanosporum and Their Significance to Truffle Cultivation in Artificially Planted Truffiéres in Australia

Abstract

Tuber melanosporum is a truffle native to Europe and is cultivated in countries such as Australia for the gastronomic market, where production yields are often lower than expected. We assessed the genetic diversity of T. melanosporum with six microsatellite loci to assess the effect of genetic drift on truffle yield in Australia. Genetic diversity as assessed on 210 ascocarps revealed a higher allelic diversity compared to previous studies from Europe, suggesting a possible genetic expansion and/or multiple and diverse source populations for inoculum. The results also suggest that the single sequence repeat diversity of locus ME2 is adaptive and that, for example, the probability of replication errors is increased for this locus. Loss of genetic diversity in Australian populations is therefore not a likely factor in limiting ascocarp production. A survey of nursery seedlings and trees inoculated with T. melanosporum revealed that <70% of seedlings and host trees were colonized with T. melanosporum and that some trees had been contaminated by Tuber brumale, presumably during the inoculation process. Mating type (MAT1-1-1 and MAT1-2-1) analyses on seedling and four-to ten-year-old host trees found that 100% of seedlings but only approximately half of host trees had both mating types present. Furthermore, MAT1-1-1 was detected significantly more commonly than MAT1-2-1 in established trees, suggesting a competitive advantage for MAT1-1-1 strains. This study clearly shows that there are more factors involved in ascocarp production than just the presence of both mating types on host trees.

Certainties and uncertainties about the life cycle of the Périgord black truffle (Tuber melanosporum Vittad.)

“…Would this be the case for artificially inoculated seedlings transplanted to field conditions? Observations made in Australia by Linde and Selmes (2012) on T. melanosporum plantations set up between 2003 and 2007 showed that out of 16 productive trees, 8 displayed only one mating type while on the remaining 8 plants, ectomycorrhizas of both mating types were present, with slightly irregular distribution. Murat et al (2013) compared two older plantations: one in Italy (Montemartano, Q. pubescens and Quercus ilex planted in 1995) and one in France (Rollainville, C. avellana, planted in 1991).…”

“…However, the close proximity of two potential mating partners is not sufficient to engage the fertilization process. Linde and Selmes (2012) showed in Australian truffle orchards that about 40% of unproductive trees sustain mycorrhizas of both mating types. Factors other than the close vicinity of compatible gametes are thus necessary for fertilization to take place.…”

“…However, while monitoring the fate of fungal strains on artificially inoculated plants the same authors found that 6 months after inoculation with T. melanosporum ascospores, almost all of the seedlings (11 of 12) had ectomycorrhizas of both mating types, while 18 months after inoculation, 7 of 12 of these seedlings had only one mating type. Linde and Selmes (2012) analysed 85 2-year-old seedlings from several Australian nurseries. All of these 2-year-old seedlings displayed ectomycorrhizas of both mating types.…”

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).…”

Black truffle cultivation: a global reality

“…The success of some plantations is threatened by the accidental introduction of T. brumale (through the imported sporocarps used as inoculum) in both countries (Linde and Selmes, 2012;Guerin-Laguette et al, 2013).…”