© Benaki Phytopathological Institute
Si increases plant resistance to pathogenic fungi
9
(Fawe
et al.,
1998). Enhanced glycosylated
phenolics and lignin activities in epidermal
cells of silicon-treated wheat reduced sever-
ity of
Blumeria graminis
f.sp.
tritici
(Belanger
et al.,
2003; Yang
et al.,
2003). Increased sil-
icon-induced resistance of rice to blast (
M.
grisea
) was related to higher production of
phytoalexin (Rodrigues
et al.,
2004; 2005).
Higher accumulation of fungitoxic pheno-
lic compounds due to silicon treatment pro-
tected
Arabidopsis
from powdery mildew
caused by
Erysiphe cichoracearum
(Ghanmi
et al.
, 2004; Fauteux
et al
., 2005). Increased
activity of antimicrobial glycosylated phe-
nolics, diterpenoid phytoalexins, and lignin
decreased severity of blast disease in sili-
con-treated rice plants (Cai
et al.,
2008). Dal-
lagnol
et al.
(2011) found that decreased lev-
el of rice brown spot
(
Bipolaris oryzae
) was
due to enhanced accumulation of lignin
and soluble phenolics. High concentra-
tions of lignin-thioglycolic acid derivatives
increased wheat resistance to blast caused
by
Pyricularia oryzae
(Xavier
et al.,
2011). Re-
garding the rice–
Rhizoctonia solani
patho-
system,
silicon-induced enhancement of
phenolic metabolism contributed to the im-
proved resistance to sheath blight of a sus-
ceptible rice cultivar (Zhang
et al.,
2013). En-
hanced production of flavonoids in wheat
leaves reduced incidence of blast
caused
by
Pyricularia oryzae
(Rodrigues
et al.,
2014).
Fortunato
et al.
(2015) found that higher ac-
tivity of total soluble phenolics and lignin-
thioglycolic acid derivatives in leaves of
soybean plants supplied with silicon led to
reduced incidence of target spot (
Coryne-
spora cassiicola).
Regarding the perennial
ryegrass–
Magnaporthe oryzae
interaction,
Rahman
et al.
(2015) found that several phe-
nolic acids, including chlorogenic acid and
flavonoids, and relative levels of genes en-
coding phenylalanine ammonia lyase and
lipoxygenase were significantly increased
in silicon-amended plants compared with
non-amended control plants. Increased
lignin concentration reduced the incidence
of
Podosphaera xanthii
(powdery mildew) in
melon plants (Dallagnol
et al.,
2015)
4.2.3. Molecular mechanism
Silicon acts as a modulator of host re-
sistance to pathogens (Fauteux
et al
., 2005;
Van Bockhaven
et al.,
2013). However, the
biochemical and physiological mechanisms
that are potentiated by silicon are complex
phenomena (Rodrigues
et al.,
2005). Under
optimum conditions, gene expression had
no significant difference between silicon-
treated and non-treated plants (Watanabe
et al.,
2004). A study by Kauss
et al.
(2003)
conducted on cucumber leaves and investi-
gating the process of plant infection showed
that resistance to infection can be acquired
by the expression of a protein rich in proline
together with the presence of silica at the
site of pathogen penetration. Fauteux
et al.
(2006) stated that only two genes were up-
regulated when silicon alone was applied
to
Arabidopsis
plants. Brunings
et al.
(2009)
studied the gene expression of silicon-treat-
ed rice using a microarray and found differ-
ential regulation of 221 genes compared to
untreated control, including some transcrip-
tion factors. Chain
et al.
(2009) demonstrat-
ed a comparable differential response with
47 genes of varying function in silicon-treat-
ed wheat. It has been suggested that sili-
con could act as a potentiator of defense
responses or as an activator of protein-me-
diated cell signaling (Fauteux
et al
., 2005;
Van Bockhaven
et al.,
2013).
It has been proposed that in a cell, silicon
controls the signaling events that guide the
synthesis of antimicrobial compounds, and
could also control the generation of system-
ic signals. In this way, silicic acid, without be-
ing a second messenger, might play a role in
resistance, both local and systemic (Fauteux
et al
., 2005; Bockhaven
et al.,
2013). By using
Agilent 44K oligo DNA arrays, it has been
shown that silicon increased significantly
the level of photorespiration in rice leaves
infected by
Cochliobolus miyabeanus
(Van
Bockhaven
et al.,
2014). Genome-wide stud-
ies on tomato, rice,
Arabidopsis
and wheat
grown in soil amendedwith silicon and com-
pared to non-amended control plants have
shown a differential and unique expression
of a large number of genes involved in host
