Plant disease and defences

• Tobacco mosaic virus (TMV) symptoms:

  • discolouration of leaves
  • mosaic pattern on leaves
  • affected part of plant cannot photosynthesise
• Tobacco mosaic virus prevention:

  • growing TMV resistant strains
  • cleaning gardening tools
• TMV is spread by direct contact with infected plants
• Rose black spot symptoms:

  • purple or black spots on leases of rose plants
  • leaves turn yellow and drop early
  • reduced growth
• Rose black spot is spread by water or wind, because the spores can be carried.
• Rose black spot prevention:

  • fungicides
  • removing and destroying infected leaves
• Signs of plant disease:

  • stunted growth
  • spots on leaves
  • discolouration
  • decay
  • malformed stems or leaves
  • abnormal growth
• Ways to identify plant disease:

  1. Look up in gardening manual or gardening website
  2. Take plant to lab
  3. Use at home testing kits, to identify pathogens using monoclonal antibodies
• Nitrate defeciency - stunts growth

  • nitrate ions are used to make amino acids, which are used to make protein
  • less protein means stunned growth
• Magnesium deficiency - causes chlorosis

  • magnesium is needed to make chlorophyll
  • chlorophyll is needed for photosynthesis, without it rate of photosynthesis slow down and leaves start to appear yellow
• Plants physical defences:

  • Waxy cuticle - barrier for pathogens
  • Layers of dead cells around stem (e.g. bark) - barrier for pathogens
  • Cellulose cell walls - barrier for pathogens around cells
• Plants mechanical defences:

  • Thorns and hairs - stops predators for eating them
  • Leaves that droop or curl when touched - knocks off insects
  • Mimicing other organisms - tricking predators into not eating them
• Plants chemical defences:

  • Antibacterial chemicals - kills bacteria and prevents disease
  • Poison - deter herbivores