The many functionalities of silicon make it a fundamental element for plants in their strategies to fight against diseases and pathogens.
After oxygen, silicon is the most abundant element in the earth’s crust, yet it is only present in small quantities in living matter. Indeed, these origins make it an element that is difficult to assimilate, hence the importance in agriculture of strengthening its assimilability by plants, whether in the form:
- biogenic, i.e. made by living things such as diatoms,
- amorphous in the sand
- mineral silica, such as quartz
- silicate, such as feldspars or kaolinite.
Want to know more ? Discover 5 good reasons to consider silicon as a major element in improving plant health.
1 / Silicon and the resistance of plant tissues
The correlation between richness in silicon and mechanical resistance of the plant is constantly observed. It results from the incorporation of silicon into the cell wall, or even deposits in the form of phytoliths or biogenic silica. This element then acts as a crosslinking agent. It improves the mechanical properties of the cell wall and guarantees the resistance of plant tissues.
2 / Fight against the effects of water stress
Silicon improves the resistance of plants to drought, by limiting the contraction of xylem vessels. The plants, grown in a medium sufficiently enriched in assimilable silicon, resist lodging and do not sag. They maintain a leaf arrangement favorable to light capture and water nutrition. Thus the proper functioning of photosynthesis promotes the growth of the plant.
3 / Prevent insect attacks
A high level of silicon in plant tissues dilutes the diet of insects such that they become unable to ingest sufficient amounts of nutrients to survive.
This element also discourages the feeding of phytophagi, thus reducing crop damage and causing a decrease in larval weight gain. Feeding larvae with compounds containing silicon causes some species to detach cells from the intestine, leading to digestive difficulties and increased mortality.
In addition, deposited as phytoliths in plants, silicon increases the hardness and abrasiveness of plant tissues, which accelerates the wear and tear of the mouth parts of phytophagous insects. It then acts as a food deterrent by reducing the digestibility of the leaves, thus reducing the negative impact of insects on crops.
4 / Carry out anti-fungal control
The references on the control of phytopathogens by silicon are mainly focused on fungal pathogens, and this on a wide range of plants. The beneficial effects of silicon were, very early on, attributed to its precipitation in the form of phytoliths in tissues, acting as a mechanical barrier.
This element has also been shown to protect the plant by stimulating other resistance mechanisms, including the accumulation of lignin, the production of phenolic compounds and defense phytoalexins.
5 / Reducing the toxicity of heavy metals
The increase in biomass, caused in particular by the addition of silicon, causes a dilution of the concentration of the metallic trace element reducing its toxic effect.
Likewise, the plant absorption of heavy metals is reduced by the physical barrier formed by the silicon phytoliths on the walls of the endoderm, leading to a decrease in the porosity of the cell walls, and thus reducing the passage of metals into the xylem.
It is possible to promote the absorption of silicon!
Increasing its availability in the soil and its quantity for plants is based on 2 strategies:
- Stimulate and / or increase the activity of PGPR bacteria (and in particular that of Bacillus) in order to increase the solubilization of the biogenic phytoliths studied in the soil.
- Provide an exogenous source of assimilable silicon to avoid any induced deficiency.
These exogenous inputs are generally applied to the soil or directly to the leaves in the form of a spray. These two strategies lead to better countering abiotic and biotic stresses, and therefore intervene in the improvement of plant health.