Plant disease - OCR Gateway Plant defences

Just like animals, plants are constantly defending themselves from attack from pathogens. Again like us, plants have physical and chemical defences which stop pathogens from infecting them and causing disease.

Physical defences

Bark - Many plants are covered with a thick bark. This is an external layer of dead cells which forms a physical barrier against infection. In this way it is very much like human skin.

Cell wall - Each plant cell has a cellulose cell wall which acts as another barrier against infection.

Leaf cuticle - Leaves are covered with a waxy cuticle which also stops their cells from becoming infected. It is a strong barrier that pathogens find it hard to pass through. This means pathogens cannot get into the tissue underneath the leaf's waxy cuticle.

Chemical defences

Some plants such as mint and witch hazel produce antimicrobial substances. These limit the spread of bacteria that were not stopped by physical defences. We now use these chemical defences in antiseptics for humans.

Other plants, like stinging nettles, have developed poisons to stop themselves being eaten by herbivores. These do not defend plants from infection by pathogens.

Other defences

Farmers can now genetically engineer crop plants to be resistant to infections.