Agriculture Reference
In-Depth Information
ton (1962) and Mankau (
1980
) with a view to establish these biocontrol agents in
soil, found somewhat negative results and concluded that biocontrol efficiency of
nematode-trapping fungi can be only satisfactory if the fungus has ability to toler-
ate ill-effects of soil fungistasis and has high degree of competitive ability. Their
interaction in soil with nematodes, plants, other organisms and the soil environ-
ment is little understood because of difficulties of working in the complex soil ma-
trix. Growth of mycelium or trap formation requires energy which can be supplied
readily available carbon and nitrogen sources consequently they concluded that ad-
dition of organic amendment to soil results in a reduction in the predaceous activity
of the fungus. This occurs because of the intensified soil microbial population com-
peting with the predaceous fungi for nutrients. They observed lysis of fungal spores
of these fungi and found none of them colonized or exploited the soil microhabitat
when placed in the soil.
In nematode-trapping fungi, germination by germ tube was hampered which gave
rise to conidial traps which induced the parasitic ability of nematode-trapping fungi.
This trapping structure formed directly with the spore, was recognized for the first
time by Dackman and Nordbring-Hertz (
1992
) as conidial trap (CT) (Fig.
12.1a, c,
e
) which has the similar ability to capture nematode, as trapping structure formed
on normal hyphae (Fig.
12.1b, d, g, f
). They believed that the CT formation in re-
sponse to soil fungistasis is a boon for nematode-trapping fungi where fungistasis
hampered the growth of many other pathogenic and non-pathogenic fungi, conidial
trap formation promotes and acts as a survival structure which gets energy from the
captured nematodes and further growth of the spores takes place in the soil.
The first attempt to use them as successful biological control was carried out
by Linford (
1937
) in his classical work where chopped green pineapple tops were
placed in nematode-infested soil in pots. They estimated the nematode population
and activity of predatory fungi after application of pineapple tops and noticed in-
crease in the number of free living nematodes in the soil as well as increase in
the stimulation of predatory fungi which killed the nematodes and brought their
population below their original level. The basic hypothesis was that the decomposi-
tion of organic substrates added to the soil increased food supply which resulted
in the multiplication of free living nematodes. These nematodes were captured by
nematode-trapping fungi, and if the capturing rate is faster than the rate of its multi-
plication, then the effect of nematode-trapping fungi declined and in the meantime
the population of plant parasitic nematodes also get reduced.
Despite their generally negative or erratic results in the past, a few recent ex-
amples of successful results have been obtained with the application of nematode-
trapping fungi. The biology, ecology and potential of these biological control agents
for nematodes have been extensively reviewed (Kerry
1987
; Stirling
1995
; Sayre
1986
; Sikora
1992
) and found that in future these nematode-trapping fungi have
very good ability to replace nematicides for the management of nematodes in dif-
ferent crops.
There are two general ways of applying nematode-trapping fungi for biologi-
cal control of nematodes—addition of large amount of inoculum in the form of
mass culture to the soil, and stimulation of activity of the pre-existing fungi using
