ABSTRACT
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A plant disease results from the intimate interaction between a plant and a
pathogen. Today, a great deal of research is devoted to the study of plant-
pathogen interactions at the cellular and molecular level. These direct
interactions are important but should not overshadow the key roles of
environmental factors, which influence these interactions and thereby
disease incidence or severity. These indirect interactions are particularly
important in the case of plant diseases caused by soil-borne pathogens.
The existence of soils that naturally suppress plant diseases (so-called
disease-suppressive soils) provides an example of soil (biotic and/or
abiotic) factors affecting the pathogen, the plant or the interaction
between the plant and the pathogen. Indeed, in suppressive soils, disease
incidence or severity commonly remain low in spite of the presence of the
pathogen, a susceptible host plant and climatic conditions that would allow
disease development [1].
