Introduction to Fungi, Third Edition

358 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.30 Epichloe typhina. (a) Tip of ascus showing the thickened apical ring pierced by a cytoplasmic canal. (b) Discharged
ascospore which has germinated to produce several phialides. (c) Phialides with primary conidia. (d) Ascospore showing
direct germination by hyphal growth. Some phialides are also visible.
not detrimentally affected and indeed may
benefit by experiencing reduced herbivory, the
relationship can be regarded as mutualistic.
The anamorphic states of Epichloe spp., now
classified as species of Neotyphodium, grow as
endophytes, i.e. symptomless symbionts, of
many grasses. Most species of Neotyphodium
produce phialoconidia in laboratory culture
and N. typhinum, the anamorph of E. typhina,
has been reported to form conidiophores on the
phylloplane (leaf surfaces) of Poa rigidifolia and
Agrostis hiemalis, although it is unclear whether
or not they are involved in horizontal transmission
in nature (White et al., 1996). What is certain
is that these endophytes are seed-borne and
are vertically transmitted. The leaf sheaths of
infected plants show a characteristic fine, intercellular,
infrequently branched, contorted mycelium
with lipid contents, running parallel to the
vascular bundles, and following the longitudinal
cell walls of the inner epidermis of the lower
leaf sheaths (Fig. 12.31). Endophyte mycelium
is less extensive in leaf blades and it is believed
that the ligule, lacking intercellular spaces,
may be a barrier to spread (Hinton & Bacon,
1985; Christensen et al., 2002). The mycelium of
Neotyphodium appears indistinguishable from
that of Epichloe. At flowering, the Neotyphodium
mycelium grows upwards through the stem,
extending into the inflorescence and infecting
the embryos of the developing seeds so that
a high proportion of them are infected (White
et al., 1991). In natural infections of Lolium perenne
by N. lolii, the mycelium is scanty in vascular
tissues but is occasionally found in smaller
vascular bundles (Christensen et al., 2001).
Alkaloids and endophytism
Intense interest in Neotyphodium has developed
since the discovery that consumption of
endophyte-infected grass is associated with disorders
of grazing livestock caused by mycotoxins,
including ergot alkaloids. Two associations
(symbiota) have been particularly well investigated.
Ingestion of tall fescue (Festuca arundinacea)
infected with N. coenophialum causes fescue
toxicosis in cattle and horses in the Southeastern
USA (Bacon et al., 1977; Blodgett, 2001). The