Agriculture Reference
In-Depth Information
4.5 CONCLUDING REMARKS
Pathogenic fungi vary greatly in the extent to which they colonise the host plant.
Advances in the techniques of molecular genetics have made significant contri-
butions to our understanding of plant-pathogen interactions (Yoder and Turgeon,
2001). In combination with optical imaging techniques, for example, expression
of green fluorescent protein (GFP) examined by confocal laser scanning microscopy
(CLSM), new structural information has been provided (Howard, 2001). The know-
ledge of cellular and genetical aspects of fungal pathogenicity and virulence
could contribute greatly to different approaches for controlling disease epidemics
in agricultural crops.
However, unsolved questions are: Why are fungi pathogens and not just
saprophytes? What are the regulation factors that are essential for the ability to
infect the host plant, or in the case of biotrophs, that are involved in retaining the
biotrophic interaction?
Pathogens have evolved strategies to overcome the plant barriers, either the
aerial plant structures or the roots. Recently, it has been shown that the rice leaf
pathogen
Magnaporthe grisea
is able to infect rice roots in a different way
compared to leaf surfaces (Sesma and Osbourn, 2004). On roots it forms infection
pads typical for root-infecting pathogens. Furthermore, it invades the vascular
system of the plant leading to systemic invasion. Interestingly, defect mutants
unable to infect rice leaves were fully pathogenic on roots, indicating that there are
clear differences between the factors required for penetration of leaves and roots.
These findings show that the fungus might be able to switch its infection strategy
and to change niches. This could be of great epidemiological significance and has
important implications for the development of new strategies for disease control.
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