Introduction to Fungi, Third Edition

342 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.17 Mycoparasitism byTrichoderma spp. (a) Tip of conidiophore of T. virens with phialides. (b) Contact of a hypha of T. harzianum
with one of Rhizoctonia cerealis. (c) Coiling of T. harzianum around a hypha of R. cerealis. (d) Intrahyphal growth of T. virens in a hypha
of Fusarium sp.
situations, entering through pruning wounds,
cracks, leaf scars and sites of branch breakage.
The colonization of the bark and cambium
tissues results in a necrotic lesion, often with
the dead heartwood visible in the centre, and
surrounded by raised callus-like bark tissue
where the tree launches a defence response.
This type of symptom is called a canker
(Fig. 12.18). Conidia and, later, perithecia are
produced in the bark of cankers. Girdling
results if a canker surrounds an entire branch,
and this leads to the death of all shoot tissue
distal to the lesion.
The conidial states of Nectria include some
terrestrial species of Fusarium, Cylindrocarpon and
Tubercularia, whilst in freshwater streams they
include the aquatic hyphomycetes Cylindrocarpon,
Flagellospora and Heliscus (Section 25.2; Webster,
1992). Some species have synanamorphic states
with conidia of distinctive size and shape, e.g.
macro- and micro-conidia (e.g. N. haematococca;
Fig. 12.19).
Nectria cinnabarina, the cause of coral spot, is
common on freshly cut twigs of hardwood trees
and shrubs, but may occasionally be a wound
parasite on these hosts. The name coral spot
refers to the pale pink conidial pustules, about
1 2 mm in diameter, which burst through the
bark (Plate 5d). Before the connection with
Nectria was understood, these conidial pustules
had been named Tubercularia vulgaris. They
consist of a column of pseudoparenchyma bearing
a dense tuft of conidiophores. These are long
slender hyphae producing intercalary phialides
at intervals along their length (Figs. 12.20b,d).
Conidial pustules of this type are termed
sporodochia. The conidia are sticky and form a
slimy mass at the surface of the sporodochium.
They are dispersed very effectively by rain splash.
Around the base of the old conidial pustule
perithecia arise (Plate 5d), and eventually the
pustule may bear perithecia over its entire
surface. Perithecial pustules develop in damp
conditions in late summer and autumn and are