Plant disease

Plants can be infected by various pathogens, including viruses (e.g., tobacco mosaic virus), fungi (e.g., black spot on roses), and insects (e.g., aphids). These infections can cause damage and reduce plant health. Additionally, plants can suffer from ion deficiencies, which can impact their growth and appearance:

• Nitrate deficiency leads to stunted growth because nitrate ions are essential for protein synthesis.

• Magnesium deficiency causes chlorosis (yellowing of leaves) since magnesium ions are needed to produce chlorophyll.

Horticulturists—people who grow and care for plants—are trained to identify symptoms of diseases and ion deficiencies, enabling them to provide the best conditions for plant growth.

Like animals, plants have developed a range of defence mechanisms to protect against pathogens and herbivores. These defences can be physical, chemical, or mechanical.

Physical Defences

These defences act as barriers to prevent pathogens from entering the plant, similar to the skin in humans:

• Cellulose cell walls provide a strong outer layer for each cell.

• Tough waxy cuticle on leaves prevents microorganisms from entering.

• Layers of dead cells around stems, such as bark on trees, provide a protective barrier that falls off, removing pathogens.

Chemical Defences

Plants also produce chemicals to protect against pathogens, similar to how stomach acid in humans helps kill microbes:

• Antibacterial chemicals: Some plants produce chemicals that kill bacteria. For example, herbs like mint and oregano contain natural antimicrobials.

• Poisons: Plants like foxglove and deadly nightshade produce toxins that deter herbivores.

Mechanical Adaptations

Mechanical adaptations help protect plants by deterring animals or tricking them:

• Thorns and hairs: Cacti and some other plants have these features to prevent animals from eating them.

• Leaves that droop or curl when touched: This movement can deter herbivores by moving the leaves out of reach.

• Mimicry: Some plants resemble other objects, like stones or pebbles, to avoid being eaten.

Horticulturists and farmers aim to keep their plants healthy and free from pathogens and pests to maximise crop yield and maintain the appearance of their plants. They have become skilled at detecting signs of disease and nutrient deficiencies in plants.

Common signs of plant diseases and deficiencies include:

• Stunted growth: This may be caused by pathogens like rose black spot or tobacco mosaic virus, or by nitrate deficiency.

• Spots on leaves: Often a sign of infections like rose black spot.

• Discolouration: Conditions like chlorosis (yellowing of leaves) can be caused by tobacco mosaic virus or magnesium deficiency.

• Areas of decay or rot.

• Growths or tumours on plant tissue.

• Malformed stems or leaves: These may be misshapen or smaller than usual.

• Presence of pests: Some pests, like aphids, are visible on plants and can spread diseases.

Gardeners and farmers use their knowledge and skills to prevent, identify, and treat plant diseases. There are several methods to identify specific diseases affecting plants:

1. Consulting gardening manuals or websites: These resources provide information on symptoms and treatments for various plant diseases.

2. Laboratory testing: Infected plants can be sent to a lab to accurately identify the pathogen.

3. Testing kits with monoclonal antibodies: These kits can detect specific pathogens, providing a quick and reliable diagnosis.

This knowledge helps in managing gardens, allotments, and fields of crops effectively.