Epichloë species are endophytic symbionts of grasses
which may differ in the relative importance of their sexual or asexual
life
cycles. Sexual reproduction of the fungus by stroma-formation prevents
host flowering (choke) and thus is highly antagonistic,
whereas asexual reproduction through clonal propagation in host seeds does
not affect host fitness. Stroma-forming Epichloë
endophytes from Bromus erectus and non-stromal strains from
B. benekenii and B. ramosus were recognized as a distinct
mating
population (MP) based on complete sexual compatibility among
strains and intersterility between other MPs established by mating
tests. This biological species represents the only documented case of
highly antagonistic strains interfertile with highly mutualistic
strains. A second distinct MP of Epichloë was evident on
Brachypodium sylvaticum including both stroma-forming and non-stromal
isolates. These two MPs were further characterized by distinct morphologies
of fruiting structures, allozyme divergence, β-tubulin
gene phylogeny, and host preferences, and were described as new species:
E. bromicola associated with Bromus spp. and E. sylvatica
with Bp. sylvaticum. Additional mating tests among Epichloë
from several, previously unexamined, hosts including Brachypodium
pinnatum, Calamagrostis villosa, Festuca spp.,
Phleum pratense, and Poa spp., expanded the known host
ranges of three other European
species, E. typhina, E. festucae and E. baconii.
Genetic variability of all five European species and gene diversity of
host subpopulations
were analysed based on allozyme data from a total of 497 Epichloë
isolates. Average gene diversity (Hs) within MPs ranged
from
0·09 to 0·36 with E. typhina being the
most diverse, and GST values, a measure for
between subpopulation differentiation, ranged
from 0·73 to 0·90 indicating that genetic isolation of
endophytes on many host grasses is likely.