Plant Diseases and Defences

• Plant diseases


  Plants can get diseases just like humans
• Mineral ions plants need


  • Nitrogen
  • Magnesium
• Nitrogen


  • Needed to make proteins and for growth
  • Lack of nitrates causes deficiency symptoms
• Magnesium


  • Needed for making chlorophyll
  • Lack of magnesium causes chlorosis and yellow leaves
• Types of pathogens that can infect plants


  • Viral
  • Bacterial
  • Fungal
• Other things that can damage plants


  • Insects like aphids
• Common signs of plant diseases


  • Stunted growth
  • Abnormal growths like lumps
  • Spots on leaves
  • Malformed stems or leaves
  • Patches of decay
  • Discolouration
• Identifying plant diseases


  1. Look up signs in gardening manual/website

  2. Take infected plant to lab for pathogen identification

  3. Use testing kits with monoclonal antibodies
• Physical defences of plants

  • Waxy cuticle on leaves and stems
  • Cell walls made of cellulose
  • Layers of dead cells like bark
• Chemical defences of plants

  • Produce antibacterial chemicals
  • Produce toxins that deter herbivores
• Mechanical defences of plants

  • Thorns and hairs to stop animals
  • Leaves that droop or curl when touched
  • Mimicry to avoid being eaten
• Plants have physical, chemical and mechanical defences
• Monoclonal antibodies can be used to identify plant pathogens