Ultramafic soils from New Caledonia structurePisolithus albusin ecotype

Abstract

Isolates of ectomycorrhizal Pisolithus albus were sampled from both ultramafic and volcano-sedimentary soils in New Caledonia, a tropical hotspot of biodiversity, to investigate the relationships between genetic diversity and edaphic constraint through tolerance to nickel (Ni). Carpophore description, spore morphology and phylogenetic analysis based on internal transcribed spacer (ITS) rDNA sequences confirmed that all isolates belong to P. albus and are closely related to other Australasian specimens. Using molecular tools, ITS-restriction fragment length polymorphism and amplified fragment length polymorphism markers, we showed the existence of two distinct genetic clusters within P. albus: ultramafic and volcano-sedimentary. Mycelia response to Ni toxicity supports such a population structure. Pisolithus albus from ultramafic soils included isolates with a high diversity of in vitro Ni tolerance, with both Ni-tolerant isolates (average Ni EC(50) at 575 microM) and Ni-sensitive isolates (average Ni EC(50) at 37 microM). In contrast, all isolates from volcano-sedimentary soils were found to be Ni sensitive (average Ni EC(50) at 32 microM). We highlight that (1) P. albus population from ultramafic soils of New Caledonia are genetically structured in ecotype, and that (2) Ni tolerance among ultramafic isolates suggests an adaptive physiological response to Ni toxicity.

Population genetics of ectomycorrhizal fungi: from current knowledge to emerging directions

“…At least three CBSs occur within Paxillus involutus that partly fit into the sexually incompatible groups previously described in the 80s by pairing monokaryons in vitro (Fries 1985;Hedh et al 2008). CBSs occur, sometimes in sympatry, within P. tinctorius Hitchcock et al 2003;Jourand et al 2010), R. vinicolor sensu lato distinguished R. vinicolor and R. vesiculosus), C. formosus (Dunham et al 2003), T. scalpturatum complex (Gryta et al 2006;Carriconde et al 2008aCarriconde et al , 2008bJargeat et al 2010), Strobilomyces (Sato et al 2007;Sato & Murakami 2008) and Scleroderma species from Africa (Sanon et al 2009). Although some EM taxa diversified by specialising on different host species, such as in the genus Leccinum (den Bakker et al 2004), in the section Deliciosi among Lactarius (Nuytinck & Verbeken 2007), in the Hebeloma crustuliniforme species complex (Aanen et al 2000(Aanen et al , 2001, in Strobilomyces species (Sato et al 2007), or among the suilloids (Kretzer et al 1996), host specificity does not seem so far to be a universal driver for EM CBS, in sharp contrast with parasitic fungi.…”

“…Similarly, using AFLP and thereafter microsatellites, Muller et al (2004 and2007, respectively) showed that there is extensive gene flow between S. luteus populations from heavy metal-polluted and nearby non-polluted soils, although individuals varied in their adaptation to heavy metals. Although this pollution had a limited effect on neutral markers, one may suppose that some selection occurs at non-neutral loci involved in adaptation to heavy metals (conversely, in P. albus, CBSs exist on ultramafic versus non-ultramafic soils; Jourand et al 2010). More generally, a part of the local genetic variability of EM populations could be driven by environmental factors (host species or ages, edaphic or climatic conditions, etc.)…”

“…Although some EM taxa diversified by specialising on different host species, such as in the genus Leccinum (den Bakker et al 2004), in the section Deliciosi among Lactarius (Nuytinck & Verbeken 2007), in the Hebeloma crustuliniforme species complex (Aanen et al 2000(Aanen et al , 2001, in Strobilomyces species (Sato et al 2007), or among the suilloids (Kretzer et al 1996), host specificity does not seem so far to be a universal driver for EM CBS, in sharp contrast with parasitic fungi. In P. involutus sensu lato, CBSs show divergent host specificity, but genomic microarrays reveal divergent gene contents that are not obviously correlated with host specificity (Hedh et al 2008); in A. muscaria form Northern America, CBSs were suggested to correlate with some habitats and/or biogeographic provinces (Geml et al 2009); in Pisolithus albus from New Caledonia, CBSs exist as an adaptation to ultramafic soils (Jourand et al 2010). Thus, no unique evolutionary base for CBSs is known for EM fungi.…”

How metal-tolerant ecotypes of ectomycorrhizal fungi protect plants from heavy metal pollution

“…Such evidence is only recently coming up for ECM fungi. Adaptive metal tolerance has been suggested for a few higher fungi, including Pisolithus tinctorius and Pisolithus albus (Egerton-Warburton and Griffin 1995; Jourand et al 2010), Suillus species (Colpaert et al 2000;Krznaric et al 2009), Cenococcum geophilum (Goncalves et al 2009) and some other ascomycetes. Ecotypes are specifically adapted against Al, Ni, Zn, Cd or Cu.…”

“…Other basidiomycete taxa that have been frequently found-but certainly not exclusively-on heavy metal-polluted soils include Hebeloma sp., Pisolithus sp. (Jourand et al 2010;Turnau et al 1988), Rhizopogon sp. (Turnau et al 1996), Scleroderma sp.…”