Annals of Applied Biology ISSN 0003-4746
EDITORIAL
Silicon in agriculture: new insights, new significance and
growing application
M.G. Keeping1,2 & O.L. Reynolds3†
1 South African Sugarcane Research Institute, Private Bag X02, Mount Edgecombe 4300, South Africa
2 School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
3 EH Graham Centre for Agricultural Innovation (New South Wales Department of Primary Industries and Charles Sturt University), Private Mail Bag,
Wagga Wagga, NSW 2650, Australia
† née Kvedaras
Correspondence
M.G. Keeping, South African Sugarcane
Research Institute, Private Bag X02, Mount
Edgecombe 4300, South Africa.
Email: [email protected]
doi:10.1111/j.1744-7348.2009.00358.x
Despite silicon’s (Si) abundance in the earth’s crust and
in soils, and its notable concentration in many terrestrial
plants, the essentiality (or at least quasi-essentiality) of
Si in basic plant biology is still contested and its general
importance largely ignored (Epstein, 1994, 1999, 2009).
However, Si is coming to the fore as a true ‘Cinderella’
element, attracting the interest of researchers from an
increasingly diverse array of fields for its evidently
valuable roles in plant nutrition, physiology and defence.
The beneficial effects of Si fertilizers on plant growth and
crop yields are now well documented in the literature,
but it is in the arena of amelioration of plant stresses, both
abiotic and biotic, that Si is showing its true potential (see
Ma, 2004; Datnoff et al., 2007 for reviews).
The abiotic stresses that Si fertilisation helps to alleviate
include drought, water logging, frost, salinity and heavy
metal toxicity (Liang et al., 2007). Biotic stresses against
which Si provides some protection include infection by
plant pathogens and herbivory by various arthropods and
vertebrates (Datnoff et al., 2007; Kvedaras et al., 2009a).
It is also becoming increasingly apparent that plants
fertilised with Si may see little benefit unless the plant is
under some form of imposed stress (Epstein, 2009). This
is evident from studies, too numerous to cite here, at the
whole-plant, physiological, cellular and molecular levels
(Fauteux et al., 2006; Kvedaras et al., 2009a). However,
Brunings et al. (2009) show that there may be important
exceptions to this, e.g. in rice, where Si may be an integral
part of rice metabolism, affecting gene regulation in the
absence of stress, and is therefore possibly essential for
this crop.
Ann Appl Biol 155 (2009) 153–154 © 2009 The Authors
Journal compilation © 2009 Association of Applied Biologists
We believe it is not premature to speculate that Si
will be shown to assist plants in resisting attack by
parasitic animals (e.g. plant-parasitic nematodes) and
plants alike. Recently, a study by Kvedaras et al. (2009b)
showed that Si can improve host plant defence via
the third trophic level by enhancing natural enemy
attraction and biological control through induced plant
defences, likely through a change in the volatile profile
produced by plants when attacked by an insect herbivore.
Research has also revealed that Si displays a marked
resemblance to plant stress hormones such as jasmonate
and salicylate in its ability to act as a modulator of induced
resistance, such that plants respond more efficiently or
earlier to pathogen or herbivore attack (Brunings et al.,
2009; Fauteux et al., 2006; Kvedaras et al., 2009a). Such
a role can only be fulfilled by Si in its soluble form
as silicic acid within the plant, and not as hydrated
insoluble (and immobile) plant silica (see synopsis of
recent evidence by Walters & Bingham, 2007). However,
this does not detract from the likely mechanical role of
plant silica, especially in grasses, as a defence against
insect herbivores. This was demonstrated most recently
by the experiments of Massey & Hartley (2009). This
raises the point that there is ample controversy within
the field of plant Si research surrounding the mode of
action (physical and/or chemical) of Si-mediated defence
of plants against pathogens (e.g. Rodrigues et al., 2004;
Walters & Bingham, 2007) and whether Si provides any
defence against vertebrate and invertebrate herbivory
(e.g. Hochuli, 1993; Vicari & Bazely, 1993; Sanson et al.,
2007). Nonetheless, the weight of evidence now leans
strongly in favour of plants using Si in an adaptive
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Silicon in agriculture
role for defence against both biotic and abiotic stresses
(Epstein, 2009).
This rich tapestry of discovery and debate within the
field of plant Si research has provided a foundation for
increasing interest in the fundamental aspects of Si’s
role in plant biology and ecology. Alongside this and
strongly linked to it, the potential for application of Si
in agriculture is growing rapidly, especially in relation
to its benefits in ameliorating environmental stresses.
Such fundamental and applied aspects formed the subject
matter for the IV Silicon in Agriculture Conference,
held from 26 to 31 October, 2008, at the Wild Coast
Sun on South Africa’s eastern seaboard near the town
of Port Edward. The papers published in this special
section form the basis of three of the plenary addresses
(out of a total of 12 such addresses) presented during
the conference, with that by Emanuel Epstein forming
part of the opening session. In this editorial, we have
cited and touched on the content of all three plenary
papers (Brunings et al., 2009; Epstein, 2009; Kvedaras
et al., 2009a). Broad subject areas covered by oral and
poster presentations during the conference included the
chemistry of Si in soils, Si and a/biotic plant stress
and various other aspects, applied and basic, of Si
in plants. The abstracts of all oral and poster papers
presented at this IV Silicon in Agriculture Conference,
along with those from the III conference in this series,
are available as freely downloadable PDFs from the URL:
http://www.siliconconference.org.za/Silicon_Links.htm.
As Si’s multifarious roles in biology and agriculture
continue to be unravelled by physiologists, soil chemists,
agronomists, cell and molecular biologists, plant pathologists, entomologists, ecologists and others, there is little
doubt that the Silicon in Agriculture Conference series
will continue as a forum for stimulating interaction and
knowledge dissemination well into the future. The next
(V) Silicon in Agriculture Conference will be held in
Beijing, China during 2011.
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Ann Appl Biol 155 (2009) 153–154 © 2009 The Authors
Journal compilation © 2009 Association of Applied Biologists