Agriculture Reference
In-Depth Information
callose deposition in tomato root cells evidenced with a GUS expressing strain of
Fusarium oxysporum
f. sp.
radicis
-
lycopersici
(Kavroulakis et al.
2005
). SAR-like
defense response induced by compost can evolve in a primed status (priming) of
plant that allow it to react immediately to future pathogen attacks. Sang et al. (
2010
)
showed as root treatments by compost water extracts, induced priming state against
C. coccodes
on pepper and
C. orbiculare
on cucumber, by enhancing PR proteins,
defense related enzyme production and H
2
O
2
generation under pathogen-inoculated
conditions. SAR strategy driven by compost is effective for a variety of plant spe-
cies, while the ability of PGPR and PGPF to promote ISR is specific to certain plant
species and genotypes (Van der Ent et al.
2009
).
8.3.2
Role of Chemicals in the Compost Suppressivity
Compost provides a number of elements, ions, organic and inorganic molecules,
originated from the abiotic matrix that may potentially affect the pathogenesis.
These factors can have a direct toxicity effect on plant pathogen growth and sur-
vival, or may indirectly contribute to diseases suppression by strengthening plant
stand.
Composts undergoing degradation, form and release a variety of substances
toxic to pathogens. Ethanol, methanol, formaldehyde, ammonia and ethyl esters
have all been identified as such substances (Bollen
1993
). Volatiles formed dur-
ing decomposition of crop residues exhibited suppressive effects on germination
of
Verticillium longisporum
sclerotia, as well as inhibition of sporulation of other
parasitic and saprophytic fungi (Bollen
1993
). Extracts of tree bark compost have
been found to release compounds toxic to fungi, i.e., inhibitors that lyse zoospores
and sporangia of
Phytophthora
sp. (Hoitink et al.
1993
). Ethyl esters of hydroxy-
oleic acids were the most toxic compounds in 6-month old composted hardwood
bark suppressive to
Phytophthora
sp. (Hoitink and Fahy
1986
). Several organic
chemicals present in composts or released by compost inhabiting microorganisms
have been identified as providing disease suppressive effects, including phenolic
compounds, volatile fatty acids and salicyclic acid (ROU
2006
). Tenuta et al. (
2002
)
found toxicity of volatile fatty acids (acetic, propionic, isobutyric, n-butyric, n-va-
leric, isovaleric, and n-caproic acids) in liquid swine manure to
Verticillium dahliae
microsclerotia. Olive mill waste composts showed the abiotic capability produced
by chemical compounds, such as phenols, for suppression of
Phytophthora
capsici
(Cayuela et al.
2008
). Ammonia, nitrous acid or volatile fatty acids accumulated in
organic amended soils with low rate of nitrification, are detrimental for
Verticillium
dahliae
microsclerotia (Tenuta and Lazarovits
2002
). This property can be imple-
mented with the use of a matter with low organic carbon content (Tenuta and Laz-
arovits
2004
). The effective NH
3
concentration was the major inhibitory component
in compost extracts of
Sclerotium rolfsii
germination (Zmora-Nahum et al.
2008
).
A nutritional-driven mechanism lead by compost is also described. For example,
N supply via compost, at agronomic levels, is beneficial to plants and functional
to physiological and structural defenses, while excessive N loading have also been
