Introduction to Fungi, Third Edition

348 HYMENOASCOMYCETES: PYRENOMYCETES
are produced by Fusarium spp. present on animal
and human feedstock (Creppy, 2002; Moss, 2002).
Zearalenone, an oestrogenic hormone from
F. graminearum, causes vulvovaginitis and infertility
in cattle and pigs, and trichothecenes such as
T-2 toxin from several other Fusarium species
cause toxic aleukia (reduction in white blood cell
count) in farm animals and humans (Joffe, 1986;
Moss, 2002).
12.4.4 Cylindrocarpon (Nectriaceae)
Fungi with Cylindrocarpon-type conidia are anamorphic
states of species of Nectria sensu lato, now
placed in a distinct genus Neonectria (Rossman
et al., 1999; Mantiri et al., 2001). The macroconidia
of Cylindrocarpon are hyaline, curved, transversely
septate phialoconidia which resemble those of
Fusarium but do not have the constricted basal
foot cell characteristic of the latter (compare
Figs. 12.21b and 12.20c). Some species also have
microconidia and some have chlamydospores.
About 120 taxa (species and varieties) have been
described and about 50 have been linked to
Nectria sensu lato. Most species of Cylindrocarpon
grow in soil and are saprotrophic or weakly
parasitic. Cylindrocarpon destructans (formerly
known as C. radicicola), whose teleomorph is
Nectria radicicola (Samuels & Brayford, 1990),
causes seedling blights and basal rots of bulbs,
as well as root rots of various plants.
Cylindrocarpon heteronema is the anamorph of
Nectria galligena, the cause of apple and pear
canker.
12.5 Clavicipitales
Fungi in this group have been and still are
assigned to various groups (Spatafora &
Blackwell, 1993; Rossman, 1996; Stensrud et al.,
2005), notably a family (Clavicipitaceae) of the
Hypocreales or a separate order (Clavicipitales).
Whatever its taxonomic rank, this group
contains fungi with several distinguishing
characteristics. Perithecia develop on a fleshy
stroma. The perithecial centrum contains a
central basal mound from which the asci arise.
Any paraphyses which develop are obliterated
by crushing as the asci enlarge (White, 1997;
Rossman et al., 1999). The asci have a well-defined
Fig12.23 Common mycotoxins produced by Fusarium spp. (a) The nonaketide zearalenone, a suspected carcinogen and
oestrogen analogue produced by F. graminearum in maize and cattle feed. (b) Fumonisin B 1
, a suspected cause of oesophageal
cancer, produced by F. moniliforme infecting maize. (c) T-2 toxin, a highly cytotoxic trichothecene (sesquiterpene derivative)
produced by F. graminearum in various cereals. (d) Vomitoxin (desoxynivalenol), a trichothecene produced by F. culmorum and
F. graminearum in maize and wheat.