infection and responce

• Plant diseases

  Caused by microorganisms including fungi, bacteria, viruses, and larger organisms like insects
• Deficiency diseases


  Caused by lack of essential minerals like nitrates or magnesium ions
• Nitrate deficiency


  • Leads to stunted growth as nitrates are needed for making proteins
• Magnesium deficiency

  • Leads to chlorosis (yellow leaves) as magnesium is needed for making chlorophyll
• Symptoms of diseased plants

  • Abnormal growths or lumps
  • Malformed stems or leaves
  • Patches of decay
  • Spots of discoloration on leaves
• Diagnosing plant disease


  1. Take basic observations

  2. Match symptoms to a disease listed in a manual or website

  3. Send sample to plant pathologist for more detailed testing
• Plant pathologist

  Specialist in plant disease who can do more detailed testing like microscopy, antigen detection, or DNA tests
• Trial and error method


  1. Try one treatment (e.g. magnesium supplement, anti-fungal spray)

  2. If it doesn't work, try something else
• Plant defenses

  • Physical
  • Chemical
  • Mechanical
• Physical defenses

  • Waxy cuticle
  • Cell walls
  • Layers of dead cells (bark)
• Chemical defenses

  • Antimicrobial substances
  • Poisons that deter or kill insects
• Mechanical defenses


  • Thorns
  • Hairs
  • Leaves that curl or droop
• Many drugs are derived from plant chemicals, including aspirin from willow trees
• Microorganisms


  A group of tiny organisms including bacteria, viruses, protists and fungi
• Pathogens

  Microorganisms that can cause disease
• Communicable/infectious diseases

  Diseases that can spread from person to person and affect both animals and plants
• How pathogens spread from person to person

  1. Through the air (e.g. coughing, sneezing)

  2. Through contaminated food and water

  3. Through direct contact
• Pathogens spread through the air

  • Influenza virus
  • Measles virus
• Pathogens spread through contaminated food and water


  • Cholera (bacterial disease spread by contaminated water)
  • Salmonella (bacteria spread by contaminated food, particularly chicken)
• Pathogens spread through direct contact

  • Athlete's foot (fungal infection spread by walking barefoot on contaminated surfaces)
• Ways to reduce the spread of pathogens

  1. Being hygienic (e.g. washing hands, cleaning cooking items)

  2. Killing vectors (e.g. using insecticides to kill mosquitoes)

  3. Vaccinating people

  4. Quarantining infected people
• The best way to prevent a pathogen from spreading is to vaccinate everybody
• Quarantine is generally only used for really serious diseases that could harm others if spread