Plant Disease and Defences

• Plants can catch diseases from

  • Fungi
  • Bacteria
  • Viruses
  • Insects
  • Lack of essential minerals (nitrates/magnesium ions)
• nitrates are proteins that plants need for growth, so plants without nitrates have stunted growth.
• magnesium ions are needed for making chlorophyll, which is needed for photosynthesis. plants with a magnesium deficiency often suffer chlorosis (yellow leaves).
• Other common symptoms:

  • Abnormal growths/lumps
  • Malformed stems/leaves
  • Patches of decay
  • Spots of discolouration on their leaves
  • Or you might be able to see the organism responsible like aphids or spider mites
• Diagnosing disease

  • Take basic observations and try to match what you see to the disease listed online or in a manual
  • Send a sample to a plant pathologist who can do more detailed testing (take tissue sample in and use a microscope to see in more detail, or look for particular antigens and pathogens)
  • Plant pathologist run DNA test
• Trial and Error

  • If plant has yellow leaves, it may have a magnesium deficiency, so attempt to give it magnesium. See if it works. If it doesn't try something else.
• Plant defences

  • Physical- physically prevent the entry of pathogens such as cellulose cell walls, waxy cuticle, layer of cells around stems (bark)
  • Chemical- chemicals the plants can secrete such as antimicrobial chemicals and poisons
  • Mechanical- more of a function than just a barrier such as thorns and hairs to stop animals eating and touching or leaves that curl or drop if insects land on them