Introduction to Fungi, Third Edition

NEMATOPHAGOUS FUNGI
679
Fig 25.5 Dactylellina haptotyla (syn. Dactylaria candida). (a) Conidiophore arising from the substrate, producing a terminal cluster of
septate spindle-shaped conidia. (b) Stalked unicellular knob traps. (c) Non-constricting ring traps. (b,c) to same scale.
surface of the ring cells. Since the inner part of
the ring wall rapidly changes shape, it is likely
that there is a slippage of microfibrils making
up the wall. Dowsett et al. (1977) showed that
the inner (luminal) wall of the ring cells in
Drechslerella (Dactylella) brochopaga is thicker than
the outer wall. The luminal wall is initially fourlayered,
but the two external wall layers rupture
during expansion.
The threefold increase in cell volume and the
commensurate increase in surface area, together
with the process of vacuolation, clearly necessitate
a rapid rearrangement of membrane material
within the cell. Heintz and Pramer (1972)
discovered a labyrinth of membrane-bound
material close to the plasma membrane on the
inside of unexpanded ring cells in Drechslerella
(Arthrobotrys) dactyloides. In expanded rings, a
more usual type of plasma membrane organization
was found, suggesting that the membranebound
inclusions had contributed to the
formation of the enlarged plasma membrane
(see also Dowsett et al., 1977).
25.1.2 Predatory fungi belonging to
Basidiomycota
Nematode-destroying basidiomycetes seem to
be confined to two closely related genera,
Hohenbuehelia and Pleurotus, both belonging to
the Pleurotaceae in the euagarics clade (p. 541;
Thorn et al., 2000). Both genera contain woodrotting
species forming clamped hyphae.
Hohenbuehelia produces a Nematoctonus anamorph
which is of relevance in nematode capture
(Fig. 25.7).
The unusual killing mechanism of Pleurotus
spp. has been described by Barron and
Thorn (1987). Hyphae produce minute unicellular
lollipop-shaped spathulate cells which secrete
droplets of a toxin-containing liquid. Various
toxins have been identified (p. 682). Nematodes
touching such a drop show dramatic symptoms
of a shrinkage of the head region and deformation
of the oesophagus. Onset of symptoms is
within one to several minutes and is quickly
followed by lethargy, so that the affected
nematode becomes immobilized close by.
Hyphae of Pleurotus show rapid tropic growth
towards orifices of the paralysed nematode, and
colonization ensues within one to several hours
(Fig. 25.7a).
Hohenbuehelia possesses two modes of parasitism.
Hourglass-shaped unicellular mycelial
branches produce a large drop of non-toxic glue
by which nematodes are trapped in the usual
predatory way (Fig. 25.7b). In addition, both