plant diseases and defences

• Rose black spot symptoms

  black or purple spots on leaves, weakening the rose plant
• Rose black spot treatment

  Using fungicides and/or removing and destroying the affected leaves.
• TMV (Tobacco Mosaic Virus)


  virus that affects plants only
• TMV treatment

  killing the plant
• 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.
• Why do plants require nitrates?

  To make proteins
• a symptom of nitrate deficiency (lack of nitrates) in a plant?

  Stunted growth - Lack of nitrates will mean that the plant can't produce proteins. As proteins are essential for growth, this means that the plant won't grow properly.
• Why do plants require magnesium?

  To make chlorophyll
• What is the main symptom of magnesium deficiency (lack of magnesium) for a plant?

  Chlorosis (yellow leaves due to lack of chlorophyll)
• List three physical changes that could indicate that a plant has a disease.

  lumps, discolouration, stunted growth
• Give three ways in which plant diseases can be identified.

  Test the DNA of the pathogens

  Use trial and error to test different treatments

  Compare the symptoms to a gardening manual or website
• What do we mean by physical defences?

  Defences that physically prevent the entry of pathogens
• name 3 physical defences

  Strong cellulose cell walls

  Layers of dead cells around the trunk (bark)

  A waxy cuticle on the leaves and stems
• What do we mean by chemical defences?

  Chemicals that plants can secrete to destroy pathogens
• 2. Chemical Defenses

  Production of antimicrobial substances

  Production of poisons that kill insects
• What do we mean by mechanical defences?

  Structures that reduce the chance of being attacked
• 3 mechanical defences

  leaves that curl or droop when insects land on them

  hairs and thorns

  mimicking other organisms to trick animals