Lateral/Strand type (Townsend and Willetts 1954; Willetts 1972). Early stage in
development of sclerotial initiation, ordinary growth of mycelium (branching, fusion
of branches, coalescence, and septation) occurs intensively (Willetts 1972). Their
morphological characteristics are identified by their specific rind and cells. Some
sclerotia have characteristic spherical black bodies protected by thick and melanic
pigmented walls, and are considered to be resistant against microbial attack during
the period of inactivity as well as to desiccation, generally 1 month to several years
(Cochrane 1958; Gray and Williams 1971; Fox 1986). The degradability or durability of sclerotia propagule is probably dependent to the ecological conditions,
which is not well known yet. The inactivated sclerotia propagules, so called “dead
sclerotia”, may become a constitution as “sclerotia grains” in soil with preserving the
unadulterated structure.
1.2 Melanized Sclerotia Grains Found in Forest Soils
Cenococcum geophilum Fr. (syn. C. graniforme Ferd. and Wing.) is one of the most
frequently encountered ectomycorrhizal (or ectoendomycorrhizal) fungi in nature
(Trappe 1962, 1964), which colonize plant roots of specific taxonomical groups
(such as Pinaceae, Fagaceae, and Betulaceae) and form symbiotic associations with
their hosts (LoBuglio 1999). As C. geophilum was originally described from its
black sclerotia by J. Sowerby in 1800 (under the name Lycoperdon graniforme), the
fungus exists not only as sterile dematiaceous mycelia but also melanized sclerotia in
forest soils (Trappe 1964; LoBuglio 1999). Even though sexual or asexual spores,
which are important taxonomic criteria in fungal classification, have never been
convincingly recorded for C. geophilum (but see Fernandez-Toiran and Agueda
2007), recent phylogenetic studies revealed that C. geophilum is monophyletic sister
group of Glonium in Dothideomycetes of Ascomycota (Spatafora et al. 2012) and
includes several genetically closely-related cryptic species (e.g., Obase et al. 2016,
2017).
Cenococcum geophilum forms ectotrophic and ectendotrophic associations with
unusually large numbers of tree, shrub, and herbaceous genera and has a worldwide
distribution including sub-tropical, temperate to arctic-alpine climatic zones (Trappe
1964; Obase et al. 2017). C. geophilum has even been observed above the Arctic
Circle in Alaska and Canadian High Arctic (75
33
0 N, 84
40
0 W) and as an important
symbiont of trees at timber line in the Washington and Oregon Cascade mountain
range (Trappe 1964, 1988; Bledsoe et al. 1989). C. geophilum is also often dominantly found in habitats exposed to high drought stress, including coastal pine forests
(e.g., Matsuda et al. 2009; Obase et al. 2011), seasonally dry woodlands (Smith et al.
2007), and volcanic deserts (Wu et al. 2005). Moreover, C. geophilum is found in
serpentine soils that have high levels of phytotoxic stress (Panaccione et al. 2001).
Sclerotia of C. geophilum, together with sclerotia of a species of Morchella, were
more numerous in burned area than a nearby unburned forest for 2 years following
fire (Miller et al. 1994). C. geophilum was able to grow in acidic soils and survive
4
M. Watanabe et al.
development of sclerotial initiation, ordinary growth of mycelium (branching, fusion
of branches, coalescence, and septation) occurs intensively (Willetts 1972). Their
morphological characteristics are identified by their specific rind and cells. Some
sclerotia have characteristic spherical black bodies protected by thick and melanic
pigmented walls, and are considered to be resistant against microbial attack during
the period of inactivity as well as to desiccation, generally 1 month to several years
(Cochrane 1958; Gray and Williams 1971; Fox 1986). The degradability or durability of sclerotia propagule is probably dependent to the ecological conditions,
which is not well known yet. The inactivated sclerotia propagules, so called “dead
sclerotia”, may become a constitution as “sclerotia grains” in soil with preserving the
unadulterated structure.
1.2 Melanized Sclerotia Grains Found in Forest Soils
Cenococcum geophilum Fr. (syn. C. graniforme Ferd. and Wing.) is one of the most
frequently encountered ectomycorrhizal (or ectoendomycorrhizal) fungi in nature
(Trappe 1962, 1964), which colonize plant roots of specific taxonomical groups
(such as Pinaceae, Fagaceae, and Betulaceae) and form symbiotic associations with
their hosts (LoBuglio 1999). As C. geophilum was originally described from its
black sclerotia by J. Sowerby in 1800 (under the name Lycoperdon graniforme), the
fungus exists not only as sterile dematiaceous mycelia but also melanized sclerotia in
forest soils (Trappe 1964; LoBuglio 1999). Even though sexual or asexual spores,
which are important taxonomic criteria in fungal classification, have never been
convincingly recorded for C. geophilum (but see Fernandez-Toiran and Agueda
2007), recent phylogenetic studies revealed that C. geophilum is monophyletic sister
group of Glonium in Dothideomycetes of Ascomycota (Spatafora et al. 2012) and
includes several genetically closely-related cryptic species (e.g., Obase et al. 2016,
2017).
Cenococcum geophilum forms ectotrophic and ectendotrophic associations with
unusually large numbers of tree, shrub, and herbaceous genera and has a worldwide
distribution including sub-tropical, temperate to arctic-alpine climatic zones (Trappe
1964; Obase et al. 2017). C. geophilum has even been observed above the Arctic
Circle in Alaska and Canadian High Arctic (75
33
0 N, 84
40
0 W) and as an important
symbiont of trees at timber line in the Washington and Oregon Cascade mountain
range (Trappe 1964, 1988; Bledsoe et al. 1989). C. geophilum is also often dominantly found in habitats exposed to high drought stress, including coastal pine forests
(e.g., Matsuda et al. 2009; Obase et al. 2011), seasonally dry woodlands (Smith et al.
2007), and volcanic deserts (Wu et al. 2005). Moreover, C. geophilum is found in
serpentine soils that have high levels of phytotoxic stress (Panaccione et al. 2001).
Sclerotia of C. geophilum, together with sclerotia of a species of Morchella, were
more numerous in burned area than a nearby unburned forest for 2 years following
fire (Miller et al. 1994). C. geophilum was able to grow in acidic soils and survive
4
M. Watanabe et al.