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Capítulo III
Introduction
The ascomycete Tolypocladium cylindrosporum (Fam. Ophiocordycipitaceae) was
first reported as a soil-borne species (Gams, 1971). Later it was found to be pathogenic to
several species of insects, including mosquito genera like Anopheles and Aedes, which are
vectors of pathogens causing human diseases such as malaria, dengue, and yellow fever
(Lam et al., 1988; Scholte et al., 2004; Weiser and Pillai, 1981). The fungus is also
pathogenic to crustaceans, and arachnids like the ticks Ornithodoros erraticus and
Ornithodoros moubata, which are vectors of African swine fever virus, and several species
of human relapsing fever borreliae (Zabalgogeazcoa et al., 2008). In addition, this fungus
has been reported as an endophyte, asymptomatically infecting the leaves of some grasses
(Sánchez Márquez et al., 2010). Other entomopathogenic fungi like Beauveria bassiana,
Lecanicillium lecanii, or Metarhizium anisopliae have also been reported as endophytes
and soil inhabitants, and they have been proposed and used as biological control agents for
invertebrate plant pests (Meyling and Eilenberg, 2007; Vega et al., 2008). The genus
Tolypocladium is also known because some of its species, T. cylindrosporum included,
produce cyclosporine A, a cyclic peptide that exhibits a strong and selective
immunosuppressive activity and is used for organ transplants (Fritsche et al., 2004).
Several families of fungal viruses have double-stranded RNA (dsRNA) genomes
encapsidated in isometric particles, but unencapsidated viruses with single-stranded RNA
(ssRNA) genomes, or single-stranded DNA (ssDNA) mycoviruses also exist (Ghabrial and
Suzuki, 2008; Yu et al., 2010). No extracellular route of infection is known for these
mycoviruses, they seem to be transmitted intracellularly during cell division, sporogenesis,
or cell fusion between compatible strains. Unlike plant or animal viruses, most known
fungal viruses seem to be avirulent, and do not produce obvious symptoms in their hosts.
Only a few mycoviruses are associated to phenotypic effects, causing hypovirulence in
fungal pathogens, disease in mushrooms, or even being beneficial, conferring thermal
tolerance to the grass host of a virus-infected endophyte (Hillman and Suzuki, 2004;
Marquez et al., 2007; Romaine and Goodin, 2002).
The presence of dsRNA molecules of viral origin has been reported in endophytic
strains of T. cylindrosporum, as well as in other species of entomopathogenic fungi such as
B. bassiana, M. anisopliae and Paecilomyces spp. (Bidochka et al., 2000; Dalzoto et al.,
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