ABSTRACT
Fungi are present in a variety of forms, in almost every habitat, where they are often specific in their occurrence on particular types of host (or substrate) and ecological niche. Fungi may also become partners with higher plants and enter complex biological relationships with the host (Clay and Kover 1996; Thrall and Burdon 1997). The term pathogen is defined as “a parasite able to cause disease in a host or range of hosts” (Kirk et al. 2001), and pathogenic fungi can occur on all plants. In this chapter this definition of plant pathogenic fungi will be limited to those that cause diseases of living plants, and therefore does not include the fungi involved in the spoilage of stored plant materials that are often referred to as causing post harvest “diseases.” The plant pathogenic fungi consist of a large group of genera and species from diverse areas of the fungal kingdom. Recent developments in the understanding of the evolution of eukaryotic organisms have meant that a number of important plant pathogenic organisms have been reclassified, and are no longer considered as fungi sensu stricto. These include the economically important genera of Phytophthom, Pythium, and other Oomycetes, that are now placed in the Straminipila (Dick 2001). Plant pathogenic fungi have a significant influence on crop productivity. Devastating fungal diseases such as corn smut, potato blight, and black stem rust of wheat can destroy many economically important crops. This situation becomes more critical when the interaction between pathogen and the host plant involves relatively long periods of intimate interaction without apparent damage to the host, and where the pathogen can persist in asymptomatic hosts for many years (Stanosz et al. 1997). The effects of fungi on living plants vary considerably. At one extreme, damage may be limited to small lesions on leaves or stems [e.g., caused by some Alternaria species, see Ellis (1968)], while at the other extreme the plant may be rapidly killed [e.g., by some Verticillium species, see Pegg (1984)].
