Introduction to Fungi, Third Edition

CLAVICIPITALES
355
alkaloid production is currently derived from
fermentations, the rest from harvested sclerotia.
The advantages of saprotrophic fermentation
are that the process can be closely controlled
and the alkaloids produced are less variable than
those from harvested ergots. A disadvantage is
that the ability to produce alkaloids in economically
significant amounts is variable and may be
lost on prolonged cultivation. Nevertheless,
the market share of alkaloids produced by
fermentation is currently increasing (Tudzynski
et al., 2001).
Control of Claviceps
The control of ergot in cereals is difficult.
Although several techniques are available, none
is completely effective. Use of ergot-free seed
would reduce infection, but inoculum may
survive from a previous crop. It can also be
provided by wild grasses bordering the field
because C. purpurea strains have wide host
ranges. Deep ploughing, which buries the sclerotia,
and crop rotation involving a non-cereal
are also helpful. Systemic fungicides would need
to be applied in sufficient amounts to produce
an effective concentration at the surface of the
ovary, and they have been used to control ergot
in seed crops of Kentucky bluegrass, Poa pratensis
(Schulz et al., 1993). Fungicide sprays are used at
present to control C. africana on sorghum in
Australia (Ryley et al., 2003) but not against
C. purpurea on cereals.
Other Claviceps spp.
Some other species of Claviceps differ in significant
ways from C. purpurea. For example,
C. fusiformis has two synanamorphs, a macroand
a micro-conidial state. Claviceps africana and
C. paspali may produce secondary phialoconidia
and these may develop in sufficient quantity on
the surface of the conidial stroma to be capable
of dispersal by wind (Luttrell, 1977; Frederickson
& Mantle, 1989; Alderman, 2003). Claviceps paspali
which infects dallisgrass (Paspalum dilatatum) is
the source of alkaloids such as paspalic acid and
its derivatives. Ingestion of its sclerotia causes
paspalum staggers in sheep. The salt marsh grass
Spartina anglica often shows heavy infection by
a specialized variety, C. purpurea var. spartinae
(Plate 5e). This fungus appears to be adapted to
an aquatic environment. Its unusually slender
sclerotia float on the surface of sea water whilst
those of other forms of C. purpurea sink. The high
levels of infection may be related to the fact that
S. anglica, an allopolyploid grass of recent origin,
is genetically uniform. Despite the heavy infection,
seed production by the host plant is not
severely affected (Raybould et al., 1998; Duncan
et al., 2002). In contrast, C. phalaridis, which is
endemic in Australia on the introduced pasture
grass Phalaris tuberosa, is systemic and when its
mycelium penetrates the inflorescence, sclerotia
are formed in all the florets, rendering the host
plant sterile (Walker, 2004). Its systemic habit
is shared by other clavicipitaceous endophytes
such as Epichloe (see below).
12.5.2 Epichloe
There are about 10 biological species (i.e. mating
populations) of Epichloe (Gr. epi ¼ on, upon;
chloë ¼ young shoots of grass) mainly infecting
cool-season grasses with the C 3 photosynthetic
pathway (Leuchtmann, 2003). They grow in
nature as biotrophic, systemic, parasitic or
symbiotic endophytes in grass shoots, forming
at first conidial, then perithecial stromata
around the uppermost leaf sheaths of tillers
containing floral primordia. Anamorphic relatives,
now classified as species of
Neotyphodium (previously Acremonium Section
Albo-lanosum; Glenn et al., 1996), are symptomless
endophytes. Neotyphodium-infected grasses
contain ergot alkaloids and other mycotoxins
which are injurious to herbivorous insects and
mammals and cause economic damage (Schardl,
1996; Kuldau & Bacon, 2001; Clay & Schardl,
2002).
Epichloe typhina (sensu lato) causes ‘choke’ of
pasture grasses and is common on grasses such
as Dactylis, Holcus and Agrostis. However, forms
of Epichloe on certain hosts are distinct from
E. typhina in dimensions of stromata, ascospores,
ascospore septation, and in molecular characteristics.
They have now been accorded different
species names. The specific name typhina should
be applied to the forms on eight genera of
grasses including Dactylis, whilst the name