developed for commercial control of the damaging
powdery mildew fungi in glasshouse crops. The host
range of Ampelomyces is restricted to the powdery
mildew fungi (Chapter 14) but it infects many of these
and is found in at least 28 countries around the world.
It has the potential to control several important dis-
eases, including powdery mildew of grapes, cucumbers,
strawberries, tomatoes, and ornamentals. Ampelomyces
produces flask-shaped pycnidia (see Fig. 2.33) that
contain many asexual spores, which are extruded
from a pore and are dispersed by water splash. These
spores germinate and directly infect the hyphae, coni-
diophores or immature sexual structures (cleistothecia)
of the powdery mildew hosts. Ampelomycesdoes not kill
the host tissues initially, but as the powdery mildew
colonies grow it produces pycnidia over the colony
surface and at this stage the host hyphae are killed.
Several cycles of infection can occur in a single growing
season, leading to significant control of the powdery
mildew hosts.
This mycoparasite survives as pycnidia between
crops or growing seasons, because it is unable to
grow in the absence of an appropriate host fungus.
This is one of the practical limitations of exploiting
Ampelomycesfor disease control, because the powdery
mildew fungi must always be present, resulting in at
least some crop damage. But this can be minimized
by applying spore formulations of A. quisqualisearly
in the growing season. The fungus is marketed com-
mercially, under the trade name AQ10™.
Necrotrophic mycoparasites
Necrotrophic mycoparasites are quite different from
the biotrophs discussed above. They have character-
istically wide host ranges and in many cases they
produce inhibitory toxins or other metabolites as part
of the parasitic process. Below, we consider three
examples to illustrate these points.
Antagonism by Clonostachys rosea(formerly
Gliocladium roseum)
Clonostachys rosea, formerly known by its asexual stage
Gliocladium roseum, is a very common soil fungus
that produces abundant asexual spores. Its sexual
stage is Bionectria ochroleuca, although this is much less
widespread than the asexual stage. C. roseacolonizes
organic matter in soil and frequently overgrows other
fungi on agar plates. In fact, the easiest way to isolate
this fungus is to sprinkle crumbs of soil onto the
colonies of other fungi: C. rosea then produces its
typical sporing structures in 8–10 days (Table 12.1).
In nutrient-rich conditions, C. roseacan kill some
fungi by producing diffusible inhibitors, but on water
agar it antagonizes the hyphae by causing localized
vacuolation and loss of turgor about 30 –90 minutes after
contact (Fig. 12.12). This is slower than hyphal inter-
ference by Basidiomycota, which can take only a few
minutes, but C. rosea also branches and coils round the
damaged compartments, so it seems to use the host
hyphae as a nutrient source. In nature C. roseais prob-
ably a secondary (opportunistic) invader of decomposing
organic matter, gaining some of its nutrients by
antagonizing living hyphae, some by exploiting dead
hyphae, and some from the underlying substratum.
A fungus called Gliocladium catenulatum is very
closely related to Clonostachys rosea(and probably
should be reclassified as Clonostachys). A strongly
antagonistic strain of this fungus is marketed by a
company in Finland (Kemira Agro OY) as a biological
control agent of several common plant diseases such
as damping off, seed rot, root rot, and stem rots.Antagonism by Talaromyces flavus
Talaromyces flavus(Ascomycota) has aPenicillium-like
asexual stage. It first attracted attention as a parasite
of Rhizoctonia solanibecause it coils round Rhizoctonia
hyphae on agar plates, penetrating the hyphae and
causing localized disruption. However recent interest
has focused on its potential to control the vascular
wilt pathogen Verticillium dahliae(see Chapter 14). It
invades the melanized microsclerotia of Verticilliumon
diseased roots, and sporulates on the surface of the
microsclerotia. T. flavusproduces up to four antibiotics
in culture, one of them being an antifungal com-
pound, talaron. However, it exerts its main effect –
at least on the hyphae of V. dahliae –by secreting
the enzyme glucose oxidase, which generates H 2 O 2
from glucose (Kim et al. 1988). Consistent with this,FUNGAL INTERACTIONS 247
Fig. 12.12Antagonism of a hyphal compartment of
Fusarium oxysporumby Clonostachys rosea. The damaged
compartment has lost its turgor but the adjacent com-
partments (top left and bottom right) are unaffected. A
narrow Fusariumhypha (arrowhead) has regrown into the
damaged compartment from a septal pore. (Courtesy of
V. Krauss.)