Polymorphism at the ribosomal DNA ITS and its relation to postglacial re‐colonization routes of the Perigord truffle Tuber melanosporum

Abstract

Summary• Glaciations and postglacial migrations are major factors responsible for the present patterns of genetic variation we see in natural populations in Europe. For ectomycorrhizal fungi, escape from refugia can only follow range expansion by their specific hosts.• To infer phylogeographic relationships within Tuber melanosporum , sequences of internal transcribed spacers (ITS) and the 5.8S coding region of the ribosomal DNA repeat were obtained for 188 individuals sampled over the entire distribution of this species in France, and in north-western Italy and north-eastern Spain.• Ten distinct ITS haplotypes were distinguished, mapped and treated using F -and N ST -statistics and nested clade (NCA) analyses. They showed a significant genetic differentiation between regional populations. NCA revealed a geographical association of ITS haplotypes, an old fragmentation into two major groups of populations, which likely colonized regions on different sides of the French Central Massif.• This re-colonization pattern is reminiscent of the one observed for host trees of the Perigord truffle, such as oaks and hazelnut trees. This suggests that host postglacial expansion was one of the major factors that shaped the mycobiont population structure.

Genetic and Phylogeographic Structures of the Symbiotic Fungus Tuber magnatum

“…Thus, when white truffle cultivation is planned in naturally productive areas, ecologically adapted truffle strains that are similar to those already present in the region should be used. Similar cautions also apply to T. melanosporum (21). The SSR markers that we used could be used to type strains of T. magnatum that are inoculated on commercially produced seedlings as well as for assessing the impact the introduced strains might have on native ectomycorrhizal populations.…”

“…Some species are widely distributed and have pronounced morphological and molecular variability (9,11,22,25,27,32), while others have a more restricted distribution and little intraspecific polymorphism in either morphological or genetic traits (3,4,8,9,26). Tuber magnatum Pico, which produces white ascomata, is harvested only in Italy and some countries on the Balkan Peninsula.In the related species T. melanosporum, there is little or no genetic differentiation between the sampled populations, and the species is regarded as one that self-fertilizes for sexual reproduction and that has an ascocarp consisting primarily of diploid (dikaryotic) hyphae (3,4,21). The few studies of genetic structure and mode of reproduction of T. magnatum found very limited intraspecific allozyme variation and a complete absence of heterozygous individuals (8).…”

“…In the related species T. melanosporum, there is little or no genetic differentiation between the sampled populations, and the species is regarded as one that self-fertilizes for sexual reproduction and that has an ascocarp consisting primarily of diploid (dikaryotic) hyphae (3,4,21). The few studies of genetic structure and mode of reproduction of T. magnatum found very limited intraspecific allozyme variation and a complete absence of heterozygous individuals (8).…”

A realized Tuber <i>magnatum</i> niche in the upper Sinni area (south Italy)

“…It is clear that genetic diversity, due to frequency dependant alleles, is geographically structured. According to the migration model from south to north (after the last glaciation) [33], we expect genetic richness in southern areas, for both host plants and fungi. It follows that we should consider Serrapotamo niche as a key site for T. magantum conservation.…”

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

“…In the most productive areas of Italy and Istria peninsula, T. magnatum showed a significant positive correlation between genetic and geographical distances and that the southernmost and northwesternmost populations were significantly differentiated from other populations (Rubini et al 2005) (Table 1). T. melanosporum had also low-level genetic diversity across its geographical range of France and Italy (Bertault et al 1998) (Table 1) but presented significant geographic differentiation among populations (Murat et al 2004; Riccioni et al 2008) (Table 1). The southernmost populations of T. melanosporum also showed higher allelic richness than the northern populations (Riccioni et al 2008).…”