Plant diseases are conditions that affect the health and growth of plants. They can be caused by various factors, including fungi, bacteria, viruses, and environmental stress. Plant diseases can reduce crop yields and cause significant damage to crops and gardens.

Chemical plant defences are compounds produced by plants to protect themselves against disease-causing agents such as fungi and bacteria. These compounds can have antimicrobial properties and help to prevent the growth and spread of disease-causing agents.

Examples of chemical plant defences include alkaloids, tannins, and secondary metabolites such as salicylic acid and jasmonic acid. These compounds can have toxic effects on disease-causing agents and help to boost the plant’s overall immunity.

Mechanical plant defences are physical structures and processes that help to protect plants against disease. These defences can include tough outer layers, such as the cuticle and bark, that prevent pathogens from penetrating the plant, as well as defence mechanisms that limit the spread of disease once it has entered the plant.

The cuticle is a waxy layer that covers the surface of leaves and stems and helps to prevent water loss. It also serves as a physical barrier that helps to prevent pathogens from entering the plant.

Plant cell walls provide structural support and help to prevent pathogens from penetrating the plant. They also play a role in defence by producing and releasing antimicrobial compounds that can help to kill or prevent the growth of disease-causing agents.

When a plant is attacked by a pathogen, it activates a defence response that helps to limit the spread of disease. This response can include the production of chemical defences, the activation of defence genes, and the formation of physical barriers to prevent the spread of the pathogen.

Systemic acquired resistance (SAR) is a defence mechanism that allows plants to protect themselves against future pathogen attacks. When a plant is exposed to a pathogen, it activates a defence response that helps to limit the spread of the disease. Over time, this response also helps to strengthen the plant’s overall immunity, making it more resistant to future pathogen attacks.