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that trapping devices are more informative than other morphological characters to
understand these nematode-trapping fungi in a better way (Liou and Tzean
1997
;
Pfister
1997
; Ahren et al.
1998
; Scholler et al.
1999
; Kano et al.
2004
). Ahren et al.
(
1998
) clustered nematode-trapping fungi into three lineages: Species with con-
stricting rings, species with various adhesive structures (net, hyphae, knobs and
nonconstricting rings) and species having no trapping devices. Based on the assimi-
lation of results obtained from morphological and molecular characters, Hagedorn
and Scholler (
1999
) and Scholler et al. (
1999
) classified nematode-trapping fungi
into four genera:
Dactylellina
species have stalked adhesive knobs characterized by
non-constricting rings with stalked adhesive knobs,
Gamsylella
species have adhe-
sive branches and unstalked knobs,
Arthrobotrys
species which is the largest group
comprising all type of adhesive networks and
Drechslerella
have only constricting
rings. Li et al. (
2005
) further converged the nematode-trapping fungi into three
groups where constricting rings forming fungi are placed in
Drechslerella,
adhesive
networks and unstalked adhesive knobs producing fungi are placed in
Arthrobotrys
and stalked adhesive knobs or unstalked adhesive knobs and stalked adhesive knobs
with non-constricting rings producing fungi are placed in
Dactylellina
.
3 Nematode-Trapping Fungi as Biocontrol Agents
The initial studies of these nematode-trapping fungi were carried out for hyphal
bail formation, attraction and predacity, mostly with bacteria feeder saprophytic
nematode
Panagrellus redivivus
. Under normal conditions, when nematodetrap-
ping fungi grow, they form normal hyphae, and when these hyphae interact with
phytonematodes, some parts of hyphae are transformed into different types of trap-
ping devices. This transformation in the hyphae takes place either due to 'nemin'
secreted by nematodes, some amino acids like valine, or sometimes even formed
spontaneously. This transformation of normal hyphae to trapping devices indicates
switching over of such fungi from saprophytic phase to predaceous phase.
According to these changes, nematode-trapping fungi are classified into two
groups, one which is sensitive group, that is fungi forming constricting rings e.g.,
Drechslerella brochopaga
where predacious ability is more but growth rate and col-
onization ability is low, while the other is insensitive group fungi forming adhesive
networks like
A. oligospora
where potential of predaceous ability is less but their
saprophytic phase and colonization ability to substrates are very good. Nematodes-
trapping fungi have been considered as promising biological agents for control of
nematodes for a long time. Their spectacular predacious behaviour on agar plates
makes them to translate those results in the field conditions. A method to assess the
variability in the predacity of nematode-trapping fungi in vitro was developed by
Heintz (
1978
). In order to select the most effective predacious fungi for soil and
field tests, the nematode capturing ability among nematode-trapping fungi is tested
first in vitro in 1:10 corn meal agar medium and most potential isolates screened out
for further testing in microcosm, pot, or field experiments.
Earlier results obtained with these nematode-trapping fungi in the soil were er-
ratic and more confusing. The work done and reviewed by Cooke (
1964
), Dudding-