Plant defence stimulators (PDS) are a class of substances that can activate or stimulate natural defence mechanisms in plants against fungi and bacteria, but generally do not have a direct biocidal effect. These substances simulate a fungal or bacterial attack, or cause the plant's defence system to react more quickly to attacks. However, they are insufficient on their own and are usually combined with treatments.
A PDS differs from a biostimulant, which helps the plant fight against abiotic stress (such as heat or water stress) rather than a pathogen.
2.4.4.a.b Natural defence using elicitors and stimulators
The origin of plant defence stimulators
PDSs can be of natural origin, as is the case for certain plant extracts, algae, oligosaccharide complexes and COS-OGA chitosan or for certain bacteria. Some PDSs are considered to be methods of biocontrol, such as several strains of Bacillus bacteria used to control powdery mildew and grey mould (Botrytis).
| NDS Types and Active ingredient | Origin | Objective |
|---|---|---|
| Plants (Fenugreek extract) | Natural | Oidium |
| Algae (Laminarin) | Natural | Oidium |
| Yeast cell wall | Natural | Mildew, Oidium and Botrytis |
| COS-OGA (oligosaccharide cocktail) | Natural | Mildew and Oidium |
| Bacillus bacteria (subtilis, amyloliquefaciens...) | Natural | Oidium and Botrytis |
Mode of action of PDSs
A PDS elicitor enables the plant to trigger its defence mechanisms directly after application. Regardless of whether the plant is infected or not, its defence system is continuously activated.
A PDS potentiator only triggers the plant's defence system when the pathogen is present. Application of the substance initially "warns" the plant, and then triggers the plant's response, quickly activating its defence mechanisms after a pathogen's attack.