Agriculture Reference
In-Depth Information
possibilities of biological engineering of nematode-trapping fungi. Identification
of new potential virulence factors is important and new technologies such as func-
tional genomics, proteomics and metabolomics will make us to identify the real
cause of infection process and to elucidate the signals which switch on the process
in the nematode-trapping fungus so that its biocontrol potential may be improved to
overcome the biotic stresses caused by phytonematodes.
Improvement of biological control agents has involved the overexpression of
lytic enzymes which is an important virulence factor in the process of infection.
Ahman et al. (
2002
) investigated the role of protease II encoding serine proteases
in host infection by generating several PII mutants. Deletion of the PII gene had
a limited effect on pathogenicity while overexpression of the gene resulted in a
higher capacity to kill nematodes. Deletion of mutant produced less traps while
multicopy transformants produced more. The strategy of biotechnology would in-
volve selection or induction of variants of potential biological control agents with
characteristics which could enhance their effectiveness. New information on host
resistance genes and nematode virulence genes provides additional insights into the
problem. Recently, several gene products have been identified which are secreted
by nematode during parasitism. In situ hybridization has been applied extensively
to study the tissue specificity and developmental expression of nematodes genes.
Though RNA interference (RNAi) has been a challenge in phytonematodes due to
thick cuticle, obligate parasitic feeding and lack of selection of transformants. Re-
cent demonstration of gene silencing with double-stranded RNA in cyst nematode
holds promises for biocontrol of these phytonematodes.
5 Concluding Remarks
A key belief to use nematode-trapping fungi for the control of phytonematodes has
largely been neglected due to its inconsistent results and less effectiveness than
chemical control. Every management practice has some limitations, and no single
approach is fool-proof. Although use of nematode-trapping fungi shows promising
results, it is better to integrate some of the management practices for the control of
phytonematodes and development of microbial consortia to overcome biotic stress
caused by them. We have also presented our conducted experiments and figures
which indicate that these nematode-trapping fungi have very good biocontrol po-
tential. Their performance can be improved from more research work and better
understanding among weak links of phytonematodes lifecycle and strong attributes
of nematode-trapping fungi during fungal and nematode interactions.
The host plant is after all the most important living entity in an agro ecosystem
and our experiments conducted on tomato, brinjal and rice show that nematode-
trapping fungi work effectively in the soil. There may be some difference in poten-
tial among isolates or different nematode-trapping fungi on the basis of sensitivity
but once these are augmented in the rhizosphere, then colonization itself reveals
their potential for restricting the damage or losses caused by phytonematodes.
