Agriculture Reference
In-Depth Information
8.3.1.4
Activation of Plant Disease-Resistance
A further suppressive mechanism, moderately introduced in the recent times, con-
cerns the induction of systemic resistance in the plants mediated by compost. It has
been stated that reduction by composts of foliar diseases, as well as all diseases in
which the site of treatment and the site of infection are spatially separated, is medi-
ated by induced resistance. A side-grafted split-root system was used to demonstrate
the occurrence of induced resistance phenomena in compost suppressing wilt dis-
ease caused by the soil-borne pathogens
Fusarium oxysporum
on melon (Yogev
et al.
2010
). While, Paplomatas et al. (
2005
) used an incised plexiglas chamber,
that allow to separate the root system in two parts, to assess induced resistance
triggered by compost in
Arabidopsis
against
Verticillium dahliae
. In response to
specific stimuli, plants are able to enhance their innate defensive capacity against a
wide spectrum of pathogens. Two distinct pathways that typically are triggered by
non-pathogenic and pathogenic microbes lead to induced systemic resistance (ISR)
and systemic acquired resistance (SAR), respectively. ISR develops systematically
via jasmonic acid and ethylene, whereas SAR signaling moves through salicylic
acid (SA) and the induction of pathogenesis related (PR) proteins, which occur
specifically during pathological or related situations. As ISR is generally driven by
useful microorganisms, in compost-grown plants it is triggered by colonization of
plant roots by plant growth-promoting rhizobacteria (PGPR) and fungi (PGPF) in-
habiting organic matter. However, many studies reported the compost-induced sup-
pressivity driven preferably by enhanced expression of the PR and defense related
genes, which share a SAR-like model. Enhanced peroxidase activity in cucumber
plants treated with pine bark compost indicated the putative role of SAR in anthrac-
nose suppression (Zhang et al.
1996
). Induced expression of two SA-dependent
pathogenesis related genes, PR-1 and β-1,3-glucanase in
Arabidopsis
grown in
compost amended soils in pathogen-free condition, conferred resistance to
Pseu-
domonas syringae
, whereas SAR deficient mutants were susceptible (Vallad et al.
2003
). Similarly, Segarra et al. (
2013a
) demonstrated with the aid of
Arabidopsis
thaliana
jasmonate insensitive and salicylic acid-deficient mutants, the need for SA
signaling in compost-induced resistance against
Botrytis cinerea
. Successively, a
microarray analyses revealed that a compost from olive marc and olive tree leaves
interfere in
B. cinerea
/
Arabidopsis
system by triggering SAR and ABA-dependent/
independent abiotic stress responses (Segarra et al.
2013b
). On the basis of several
receptor-like kinase upregulated genes in compost-grown plants, has been more-
over hypothesized that compost might be recognized as PAMPs or MAMPs. These
are pathogen or microbe associated molecular patterns involved in pathogen recog-
nizing by receptors located in the plasma membrane of the plant cell as stated by
Cassells and Rafferty-McArdle (
2012
).
This model is believed to be also implied in the development of structural bar-
riers in the plants against pathogenic infections. Compost water extracts applied to
roots, elicited lignin accumulation in pepper stems against aerial infections of
Phy-
tophthora capsici
or
Colletotrichum coccodes
(Sang et al.
2010
). While, a compost
derived from agricultural residues promoted the pathogen exclusion by inducing
