Articles
THE USE OF SUPPRESSIVE SOILS AS SUBSTRATE FOR ORNAMENTAL AND FLOWERING PLANTS (*)
Two different broad types of diseases suppressiveness are recognized: natural and induced.
Natural suppressiveness is frequently associated with the physical properties of soils and is relatively indipendent of crop history.
On the contrary, induced suppressiveness is wholly dependent on agricultural practices.
The isolation, identification and culture of the antagonistic microorganism(s) responsible for suppressiveness in soils opens up the exciting possibility for controlling plant diseases by adding these antagonists to previously conducive soils or substrates.
Some examples of soils and substrates suppressive against soilborne pathogens are discussed with special attention to Fusarium-suppressive soils and to the use of composted bark.
The presence of a pathogenic microoganism in a substrate is not alone sufficient to cause severe disease in a susceptible host.
The nature of the substrate and the physiological state of the host must also be favourable to disease development.
The composition of the substrate has been shown in recent years to have an overriding influence on disease intensity.
The term "disease suppressiveness" is commonly used to designate agricultural soils or substrates, where certain specific soil-borne diseases are absent or occur only to a low degree, when the pathogen is present naturally or artificially introduced (Schroth and Hancock, 1981). The inhospitality of these "suppressive" soils to some plant pathogens is such that either the pathogen cannot establish or they establish but fail to produce disease or they establish and cause disease at first but diminish with continued culture of the crop (Baker and Cook, 1974). These reaction groups are used for convenience and do not imply that the three phenomena are regulated by distinct biological principles.
The phenomenon of soil suppressiveness is well known from a long time: for example investigations on Fusarium-suppressive soils started more than 60 years ago.
Knudson and Volk in 1922 began