Agriculture Reference
In-Depth Information
the context of diseases caused by telluric pathogens. At any rate, there are several
interesting studies on the application of composts and their derivatives, to suppress
aerial plant diseases. In the large landscape of the different available approaches
that may be used to prevent, mitigate or control plant diseases, the use of suppres-
sive composts may be referred in total as a biological control tool. It, in fact, fully
corresponds to U.S. National Research Council definition of biological control:
“the use of natural or modified organisms, genes, or gene products, to reduce the
effects of undesirable organisms and to favor desirable organisms such as crops,
beneficial insects, and microorganisms” (Pal and McSpadden
2006
). Accordingly
to that, compost suppressivity may be assured by microbial communities, that may
play antagonistic functions but, also, by organic molecules that may be ascribed as
microbe “gene products”.
8.2
The Concept of Compost Suppressivity
The ability of compost to generate an environment partially or totally adverse to the
development of plant disease(s), although a pathogen might be present and the host
plant is susceptible to it, is defined suppressivity. Generally, to indicate this prop-
erty, in the field of phytopathology, in addition, is also used variables of the term
suppressivity bearing the same root (i.e., suppressiveness, suppressive, suppression,
etc.), and/or its synonym such as repressiveness. The establishment of condition(s)
exactly opposite to those indicated for suppressivity occurrence is named conduc-
tivity. Thus, conductive composts are those that favor the development of plant
pathogen(s) and/or plant disease(s). The compost that does not affect any phyto-
pathological parameter is reported to be null effect.
The theory of disease suppressivity related to the compost is borrowed from that
of the natural suppressive soils (Haas and Défago
2005
). Although, in this case, it
were principally referred to the suppression of soil borne plant pathogens (Mazzola
2002
), in the particular case of compost, it has also been extended to the aerial and
seed-borne diseases control ability.
In the compost different components co-exists both biotic and abiotic ones that,
potentially, might sustain in varying degree the suppressive functions. Based on
how the different determinants concur to realize it, compost suppressivity has also
been described according to a more informative classification that include biotic or
abiotic, general or specific and, finally, direct or indirect suppressivity. Hence, this
further separation, evidently, is closely related to the mechanisms of action of the
compost. Therefore, hereinafter, we will report only the definitions, reserving the
details in the specific paragraphs.
8.2.1
Biotic and Abiotic Suppressivity
This primary distinction is much important and emphasizes the contribution of-
fered by living microorganisms against that, instead, provided by the organic and
