B3 Plant diseases and defences

• Symptoms of disease

  discolouration

  Decay

  Abnormal growths

  Malformed stem

  Spots on leaves

  stunted growth

  visible pests
• How to identify disease

  refer to gardening website or manual

  Lab tests

  Home testing kit that uses monoclonal antibodies
• Causes of diseases in plants

  pathogens - bacteria, virus, fungi

  insects

  ion deficiency diseases
• Tobacco Mosaic virus - VIRUS

  Mosaic pattern of discolouration on the leaves, this reduces growth
• Rose black spot - FUNGUS

  Purple or black spots on the leaves, which turn yellow and drop off

  This reduces growth
• Aphids - INSECTS

  Mottled or yellow leaves, wilting and slow growth rate.

  Visible pests seen
• Nitrate Deficiency

  Stunted growth is the main symptom

  Nitrate ions are needed to make amino acids

  Amino acids are used to make protein

  Protein is essential for growth
• Magnesium Deficiency

  Yellow leaves (chlorosis) is the main symptom

  Magnesium is needed to make chlorophyll and the plant cant make enough

  Leads to stunted growth due to lack of photosynthesis
• Physical defences - reduce invasion by microorganisms

  Thick bark on trees

  Cellulose (cell walls)
• Chemical defences

  Poisonous/ toxic chemicals released

  Nettle - releases acid (neutralisation)
• Mechanical adaptations

  Hairs and thorns