Introduction to Fungi, Third Edition

CLAVICIPITALES
357
Fig12.29 Epichloe baconii. (a) T.S. stem and leaf
sheath of Agrostis surrounded by a perithecial stroma.
Note the axillary shoots between the leaf sheath and
the stem. (b) Part of the conidial stroma. (c) A single
perithecium. Note the periphyses lining the ostiole.
(d) Ascus and ascospores. Note the apical apparatus
of the ascus.
which may feed on perithecia and so reduce
ascospore production (Welch & Bultman, 1993).
12.5.3 Epichloe-related grass endophytes
White (1988) has classified the relationships
between Epichloe or related endophytes and
their hosts into three types. In type I associations,
perithecial stromata are formed on the inflorescences
of most if not all infected individuals
so that flowering of the host is suppressed.
Dactylis glomerata and Agrostis tenuis harbour this
type of association which should be regarded
as parasitic. In type II associations, stromata
are formed on only a few (1 10%) of infected
individuals in a population, although 50 75% of
the population may contain the infection. This
type of association has been found only in the
sub-family Festucoideae. Agrostis hiemalis, Bromus
anomalus and Elymus canadensis have associations
of this type. The endophyte is probably spread
by clonal (i.e. vegetative) growth of the infected
host, by ascospores (contagious or horizontal
transmission) and by seed transmission (vertical
transmission). In type III associations, stromata
are not formed on infected plants and apparently
are never produced. Such associations
have been found only in festucoid grasses including
tall fescue (Festuca arundinacea) and perennial
ryegrass (Lolium perenne). In many of these grasses
over 90% of individuals are infected. In this type
of association the endophytes rely on vertical
transmission which involves mycelial growth
from the parent plant to the embryo within the
seed (White et al., 1991). Since the host plant is