© Benaki Phytopathological Institute
Sakr
10
plant defense mechanisms or metabolism
(Watanabe
et al.,
2004; Fauteux
et al.,
2006;
Chain
et al.,
2009; Brunings
et al.,
2009; Gha-
reeb
et al.,
2011).
5.
In vitro
inhibition of fungal patho-
gens by soluble silicon
Some studies have been carried out to de-
termine whether silicon has fungicidal ac-
tivity
in vitro
. Hyphal growth of
Magnopo-
rthe grisea
on silicic acid-amended water
agar was 62% less compared to growth on
non-amended water agar (Maekawa
et al.,
2003). Bekker
et al.
(2006) reported that my-
celial growth of 11 phytopathogenic fungi
(
Phytophthora cinnamomi, Sclerotinia scle-
rotiorum, Pythium
F-group,
Mucor pusillus,
Drechslera
spp.,
Fusarium oxysporum, F. so-
lani, Alternaria solani, Colletotrichum coc-
codes, Verticillium theobromae, Curvularia
lunata
and
Stemphylium herbarum
) was in-
hibited on potassium silicate (20.7% Si0
2
)-
amended PDA, at concentrations ≥ 20 ml
Si/l agar. The level of mycelial inhibition was
dependant on dose indicating different tol-
erance of the tested fungi to potassium sil-
icate. Bi
et al.
(2006) reported that 100 mM
sodium silicate completely inhibited myce-
lial growth of
Alternaria alternata
,
F. semi-
tectum
, and
Trichothecium roseum
. Sodium
silicate inhibited spore germination and my-
celial growth of
Penicillium digitatum (Liu
et al., 2010).
Nevertheless, Shen
et al.
(2010)
indicated that the inhibition of
Rhizocto-
nia solani
,
F. oxysporum
,
F. oxysporum
f. sp.
fragariae
and
Pestalotiopsis clavispora
col-
ony growth on PDA plates amended with
low concentrations of potassium silicate
(1.67, 3.33, 5 or 6.67 mM) was due to a pH
effect. The range of potassium silicate con-
centrations tested is suitable for field appli-
cation (Shen
et al.,
2010). Also, the potassi-
um silicate concentrations used by Bekker
et al.
(2006) were 50 to 60 times higher than
those in Shen’s
et al.
(2010) study. Moreoev-
er, these concentrations (Bekker
et al.,
2006;
Bi
et al.,
2006) are unrealistic for field use be-
cause the high pH of the resulting potassi-
um silicate solutions could cause phytotox-
icity. Shen
et al.
(2010) concluded that the
reduction in fungal diseases following treat-
ment of field plants with silicon is proba-
bly not due to the fungistatic effects of sil-
icon, but to other biochemical and physical
mechanisms mentioned previously.
6. Conclusions
Silicon application could be one of the most
promising approaches for sustainable, en-
vironmentally sound and broad-spectrum
control of fungal diseases in plants in various
agricultural contexts. That is why in the last
few decades, extensive studies have been
carried out to investigate its protective role
in numerous pathosystems. However, its ef-
fect on enhancing plant resistance against
fungal pathogens is not limited to high sil-
icon-accumulators as it has also been de-
scribed in low silicon-accumulators. The role
of silicon as a modulator of plant defense-re-
lated gene expression in combination with
biotic stress is dominant over its function as
a mechanical barrier. Silicon does not seem
to directly affect phytopathogenic fungi, as
fungicides, and therefore exerts no selective
pressure. The in-depth understanding of sil-
icon in plants will be helpful to effective-
ly use silicon to increase crop yield and en-
hance resistance to fungal pathogens.
I would like to thank Professor I. Othman, Di-
rector General of AECS, and the Head of the
Agriculture Department for their support.
Literature cited
Arnon, D. and Stout, P. 1939. The essentiality of cer-
tain elements in minute quantity for plants with
special reference to copper.
Plant Physiology
, 14:
371-375.
Arsenault-Labrecque, G., Menzies, J.G. and Belanger,
R.R. 2012. Effect of silicon absorption on soy-
bean resistance to
Phakopsora pachyrhizi
in dif-
ferent cultivars.
Plant Disease
, 96: 37-42.
Bayles, R.A., Flath, K., Hovmoller, M.S. and de Valla-
