1.1 Sclerotia: Fungal Propagule or Soil Grain?
Sclerotia are fungal resting structures, or persistent propagules which can germinate
to produce mycelia, asexual spores of sporocarps such as apothecia in which sexual
spores are borne (Coley-Smith and Cooke 1971). Mycelium of fungal species such
as Deuteromycetes, Ascomycetes, and Basidiomycetes are known/believed to form
sclerotia. Their structure enables them to survive periods of adverse conditions,
which are too severe for the ordinary vegetative mycelium, such as undernutrition,
low temperature, and desiccation. The growth of sclerotia proceeds to sexual
reproduction at increased nutritional levels (Ferdinandsen and Winge 1925;
Cochrane 1958; Scheidegger and Brunner 1995). Sclerotization is evaluated as an
important method to preserve culture collections in long term with advantages of low
cost and low maintenance (Nakasone et al. 2004).
Sclerotia-forming fungi are ecologically diverse and many unrelated fungi with
diverse trophic modes may form sclerotia (Smith et al. 2015). Sclerotia have
attracted research interests of botanist, mycologist, cytologist, histochemist, and
phytopathologist for a long time. Figure 1.1 shows the needle leaves Cryptomeria
japonica infected with black oval-shaped sclerotia of Scolicosporium sp.
Sclerotium-forming fungi are excellent targets for the discovery of antibacterial,
antifungal, and anti-herbivore compounds (Smith et al. 2015). According to
Townsend and Willetts (1954), many diseases of crops are caused by those fungi
which normally produce sclerotia at some time in their life history. These sclerotia
were recognized with great biological and phytopathological importance since they
serve themselves as vegetative reproductive bodies, or reproductive structures
developed from themselves. Many researches under such interests had been reported
on various species: Rhizoctonia solani (Naiki and Ui 1969, 1975, 1977), Sclerotinia
sclerotiorum (Maxwell et al. 1970; Saito 1977), Sclerotinia minor (Bullock et al.
1980a, b, 1983), Sclerotinia fructigena (Calonge 1968), Sclerotium rolfsii (Chet
et al. 1967, 1969), Pisolithus tinctorius (Grenville et al. 1985a), Hebeloma
Fig. 1.1 The dead branch of Cryptomeria japonica (left) and their needle leaves infected with
black oval-shaped sclerotia of Scolicosporium sp. (right)
2
M. Watanabe et al.
Sclerotia are fungal resting structures, or persistent propagules which can germinate
to produce mycelia, asexual spores of sporocarps such as apothecia in which sexual
spores are borne (Coley-Smith and Cooke 1971). Mycelium of fungal species such
as Deuteromycetes, Ascomycetes, and Basidiomycetes are known/believed to form
sclerotia. Their structure enables them to survive periods of adverse conditions,
which are too severe for the ordinary vegetative mycelium, such as undernutrition,
low temperature, and desiccation. The growth of sclerotia proceeds to sexual
reproduction at increased nutritional levels (Ferdinandsen and Winge 1925;
Cochrane 1958; Scheidegger and Brunner 1995). Sclerotization is evaluated as an
important method to preserve culture collections in long term with advantages of low
cost and low maintenance (Nakasone et al. 2004).
Sclerotia-forming fungi are ecologically diverse and many unrelated fungi with
diverse trophic modes may form sclerotia (Smith et al. 2015). Sclerotia have
attracted research interests of botanist, mycologist, cytologist, histochemist, and
phytopathologist for a long time. Figure 1.1 shows the needle leaves Cryptomeria
japonica infected with black oval-shaped sclerotia of Scolicosporium sp.
Sclerotium-forming fungi are excellent targets for the discovery of antibacterial,
antifungal, and anti-herbivore compounds (Smith et al. 2015). According to
Townsend and Willetts (1954), many diseases of crops are caused by those fungi
which normally produce sclerotia at some time in their life history. These sclerotia
were recognized with great biological and phytopathological importance since they
serve themselves as vegetative reproductive bodies, or reproductive structures
developed from themselves. Many researches under such interests had been reported
on various species: Rhizoctonia solani (Naiki and Ui 1969, 1975, 1977), Sclerotinia
sclerotiorum (Maxwell et al. 1970; Saito 1977), Sclerotinia minor (Bullock et al.
1980a, b, 1983), Sclerotinia fructigena (Calonge 1968), Sclerotium rolfsii (Chet
et al. 1967, 1969), Pisolithus tinctorius (Grenville et al. 1985a), Hebeloma
Fig. 1.1 The dead branch of Cryptomeria japonica (left) and their needle leaves infected with
black oval-shaped sclerotia of Scolicosporium sp. (right)
2
M. Watanabe et al.