Plant Diseases and Plant Defences

Plant Diseases and Plant Defences

Plant Diseases

Types of Plant Diseases

  • Fungal diseases: These are caused by fungi and include diseases like powdery mildew, blight and rusts.
  • Viral diseases: Caused by viruses, these diseases can have severe impacts on plants such as yellow mosaic disease in beans.
  • Bacterial diseases: Caused by bacteria, these diseases can lead to rotting or wilting of plants.

Symptoms of Plant Diseases

  • Yellowing of leaves: Clinically known as chlorosis, it may indicate a nutrient deficiency or disease.
  • Leaf spots: These can indicate a fungal or bacterial infection.
  • Wilting: If it is not related to water supply, wilting may indicate a disease.
  • Stunted growth: Poor or stunted growth often indicates a disease or pest attack.

Plant Defences

Physical Defences

  • Tough leaves: Some plants have tough or leathery leaves that are hard to eat and digest by herbivores.
  • Thorns, spikes, and hairs: These features serve to deter herbivores.
  • Bark: The bark of a tree acts as a physical barrier against pests and diseases.

Chemical Defences

  • Poisonous chemicals: Some plants produce toxic chemicals to deter herbivores or kill them.
  • Antibacterial chemicals: Plants can produce chemicals that inhibit bacterial growth or kill bacteria.

Plant Responses to Invaders

  • Localised response: The infected area may undergo cell death to limit the spread of disease.
  • Systemic acquired resistance (SAR): This is a ‘whole-plant’ resistance response that occurs following an earlier localized exposure to a pathogen.

Impact of Plant Diseases

  • Diseases can significantly impact plant health and productivity, leading to losses in agricultural yield.
  • Biodiversity is affected when plant diseases affect a particular species in large numbers.
  • Some plant diseases can also affect human health, such as ergot caused by a fungus in rye crops.

Disease Control in Agriculture

  • Use of fungicides, bactericides or insecticides: These chemicals kill or inhibit growth of the disease-causing entity.
  • Breeding resistant varieties: By means of genetic modification, plant varieties resistant to certain diseases can be developed.
  • Farm hygiene: Removing plant debris and regular inspections can prevent the spread of disease.

Revising the topics of plant diseases and plant defences is essential for understanding the broader impacts on global agriculture and biodiversity. By understanding the methods of disease control, we can also grasp the links to genetic modification and the wider debates on its uses and effects.