Agriculture Reference
In-Depth Information
CHAPTER 4
INFECTION STRATEGIES OF PLANT PARASITIC FUNGI
C. STRUCK
4.1 INTRODUCTION
How plant pathogens attack their host plants is one of the most interesting questions
in plant pathology. Numerous fungi and fungus-like organisms cause some 10,000
different diseases in plants (Pennisi, 2001). Fungal diseases of plants cause eco-
nomic losses by reducing seed germination, destroying plants or the harvesting
products and by secreting secondary metabolites that are toxic for man and animals.
Successful colonization of the habitat plant, including uptake of nutrients and
reproduction, greatly depends on an efficient mode of infection. Plant parasitic fungi
have developed various strategies to enter their hosts, and to establish direct contact
with them. Successful interactions result in devastating plant diseases. In many cases
this means the production of very large amounts of spores that are wind dispersed
from one susceptible host to another. Furthermore, there are several examples
described of long-distance dispersal of fungal spores by wind that can spread plant
diseases across and even between continents and allow invasion into new territories
(Brown and Hovmøller, 2002).
The infection mechanisms of pathogenic fungi are highly variable. During the
early phases of the infection process before invading the plant tissue, the
development of fungi greatly depends on favourable environmental conditions such
as surface moisture, relative humidity, temperature and light. In some cases, the
supply of nutrients on the surface may also have an influence on germination.
Morphogenetic and physiological differentiation of the invading fungus depends
on the mode of penetration. The infection process consists of a number of morpho-
logically more or less distinguishable stages: spore germination, formation of an
appressorium and a penetration hypha that penetrates the cuticle and the cell wall
(Mendgen
et al.
, 1996). Within the host tissue, pathogenic fungi develop infection
hyphae and some biotrophs form haustoria. A review of this subject with more
details on cell biology is given by Hardham (2001).
The diverse strategies that fungal pathogens use to infect their host plants are
becoming much better understood by means of molecular genetics techniques that
have allowed the identification of fungal genes which are crucial to disease
development.
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