© Benaki Phytopathological Institute
Sakr
4
nitrogen (Rodriges and Datnoff, 2005). The
majority of dicotyledonous plants, such as
cucumbers, melons, strawberries, and soy-
beans, absorb silicon inertly (Ma and Yamaji,
2006). Nonetheless, some plants, especially
dicotyledons, such as tomatoes, beans, and
other plant species, are not able to absorb
silicon from soil (Ma and Yamaji, 2006). The
Si/Ca ratio is another criterion used to deter-
mine whether a plant species is classified as
a silicon absorber (Datnoff
et al
.
,
2007).
3. Silicon controls fungal plant
pathogens
In plant species, the association between sil-
icon and reduced severity of fungal diseas-
es has been documented in several studies.
Another interesting association is the seem-
ingly stronger efficacy of silicon against bi-
otrophic and hemibiotrophic pathogens
(e.g. rice blast, powdery mildews) compared
to necrotrophs (Belanger
et al.,
2014).
Adding silicon to plants as a fertiliz-
er makes them more resistant to various
pathogenic fungi (Datnoff
et al.,
2007). There
are several silicon fertilizers (solid and liquid
sources) that could be used for agronom-
ic purposes (Heckman, 2013; Datnoff and
Heckman, 2014). To be beneficial for plants,
silicon fertilizers should provide a high per-
centage of silicon in a soluble form, be cost
effective, have physical properties that will
facilitate storage ability, ease their applica-
tion, be uncontaminated with heavy met-
als, and perhaps have the ability to raise soil
pH (Heckman, 2013; Datnoff and Heckman,
2014). Calcium silicate (CaSiO
3
) incorporated
into soil has been used successfully as a sol-
id source. Liquid sources, which are primar-
ily used as a foliar spray, include potassium
silicate (K
2
SiO
3
) or sodium silicate (Na
2
SiO
3
).
Silicon has proved effective in controlling
both soil- and air-borne fungal diseases in
several plant crops.
3.1. Air- and soil- borne fungi
Numerous studies have shown increased
plant resistance to foliar fungal pathogens
as a response to silicon application. For ex-
ample, soil treatments with silicon-rich ma-
terials reduced the incidence of diseases
caused by
Erysiphe graminis
(powdery mil-
dew) and
Septoria nodorum (
leaf and glume
blotch
)
on wheat, as reported by Leusch and
Buchenauer (1989)
.
Foliar sprays of potassi-
um silicate at concentrations ≥17 mM effec-
tively reduced the number of powdery mil-
dew (
Sphaerotheca fuliginea on
cucumber
and muskmelon
; Erysiphe cichoracearum on
zucchini squash
)
colonies on leaves (Men-
zies
et al.,
1992). Bowen
et al.
(1992) also re-
ported that foliar sprays of potassium sil-
icate at 1.7 mM reduced the number of
powdery mildew (
Uncinula necator
) colonies
on grape leaves by more than 60%. Soil
sili-
con fertilization at 100 mg/l appeared to in-
crease wheat resistance to
Blumeria graminis
(powdery mildew),
Mycosphaerella gramini-
cola
(septoria leaf blotch),
Phaeosphaeria
nodorum
(leaf spot), and
Puccinia recondita
(brown rust) only under high disease pres-
sure (Rodgers-Gray and Shaw, 2004). A 40%
reduction in the incidence of neck blast (
Py-
ricularia oryzae
) on rice plants supplied with
silicon was reported by Seebold
et al.
(2004).
Foliar application of 1% sodium metasili-
cate solution to sweet cherry reduced blue
mold decay (
Penicillium expansum
) by 63%
and brown rot decay (
Monilinia fructicola
) by
87% (Qin and Tian, 2005). The root applica-
tion of silicon reduced powdery mildew se-
verity on cucumber (Liang
et al.,
2005). Po-
tassium silicate application to soil reduced
strawberry powdery mildew (
Sphaerothe-
ca aphanis
) by 86% in the first year and by
60% in the second year (Kanto
et al.,
2006).
In the
Colletotrichum lindemuthianum
-bean
pathosystem, silicon reduced both the area
under the anthracnose incidence progress
curve and the area under the anthracnose
severity progress curve (Moraes
et al.,
2006).
Root applications of 1.7 mM Si reduced the
severity of powdery mildew disease (
Blume-
ria graminis
f. sp.
tritici
) on wheat by as much
as 80% (Guevel
et al.,
2007). Guo
et al.
(2007)
reported that sodium silicate reduced signif-
icantly the severity of post-harvest pink rot
of Chinese cantaloupe caused by
Trichoth-
