3.11 - Plant Diseases and Defences

• Three main causes of plant diseases:

  • infection by microorganisms such as fungi, bacteria or viruses
  • attack by larger organisms, such as insects
  • lack of essential minerals, such as nitrates or magnesium ions
• Common symptoms of diseases in plants:

  • abnormal lumps/growths
  • patches of decay
  • discolouration on leaves
  • malformed stem/leaves
• Physical Plant Defences:

  • waxy cuticle (on leaves and stems)
  • cellulose cell walls
  • layers of dead cells (bark)
• Chemical Plant Defences:

  • antimicrobial substances being secreted
  • poisons being secreted
• Mechanical Plant Defences :

  • thorns and hairs
  • leaves that curl or droop when insects land on them
• Why do plants require nitrates?

  To make proteins
• What is a symptom of a nitrate deficiency in a plant?

  Stunted growth
• Why do plants require magnesium?

  To make chlorophyll
• What is the main symp of a magnesium deficiency in plants?

  Chlorosis (yellow leaves due to lack of chlorophyll)
• What are some ways in which plant diseases can be identified?

  • Comparing the symptoms to a gardening manual or website
  • Take the infected plant to a laboratory
  • Use testing kits that contain monoclonal antibodies made
  • Test DNA of pathogens