Plant disease

• What types of pathogens can infect plants?

  Bacterial and viral pathogens
• Which insects are known to infest plants?

  Aphids
• What effect do aphids have on plants?

  They weaken the plant by removing phloem sap
• What role do aphids play in disease transmission?

  They act as vectors for disease transfer
• What are the methods to control aphid infestation in plants?

  • Biological pest control using ladybirds
  • Chemical pesticides
• What is a natural predator of aphids?

  Ladybirds
• Why is biological pest control effective against aphids?

  It uses natural predators to reduce aphid populations
• How do aphids feed on plants?

  They pierce the stem and access phloem sap
• What is the purpose of chemical pesticides in controlling aphids?

  To kill aphids and reduce their numbers
• what are aphids and what do they have?

  • insects
  • long sharp mouthpieces that pierce the surface of the stem and into the phloem so that they can feed on the sugar filled sap
  • they can infest a plant in large numbers and remove large quantities of the phloem sap, this can weaken the plant
  • aphids can act as a vector for the transfer of diseases
  • Biological pest control (using ladybirds, a natural predator of the aphid) to feed on them or using chemical pesticides are the best ways to control infestation with aphids
• what are symptoms of rose black spot?

  • stunted growth
  • spots on leaves
  • areas decaying/rotting
• what are symptoms of tobacco mosaic virus?

  • stunted growth
  • discolouration of leaves
• what are symptoms of mineral deficiencies?

  • stunted growth
  • discolouration of leaves
• what is a symptom of potato blight?

  • areas decaying/rotting
• what are symptoms of aphids and caterpillars?

  • visible pests
• what's a symptom of aphid infestation?

  • malformed stems and leaves
• • The symptoms of plant diseases can apply to more than one disease, which makes identifying them difficult
  • Diseases in the garden can be identified by comparing symptoms to those described in gardening manuals or online
  • Crop plants or forest trees, experts may visit the field/woodland to take samples which can then be taken to a lab to undergo DNA analysis. This would help to identify the specific pathogen causing the problem
  • Plant scientists, foresters, farmers and market gardeners can use testing kits which contain monoclonal antibodies to identify the presence of pathogens quickly and easily
• What are mineral deficiencies?

  • Plants like all organisms need the correct amount of nutrients to function properly
  • If plants are deficient in a mineral these can be replaced by fertilisers added to the soil
  • These fertilisers are often shown as NPK ratios depending on the need of the plant that is being grown
• what's the use of nitrates in plants?

  • production of amino acids for proteins
• what are the symptoms of a nitrate deficiency?

  • stunted growth
  • upper leaves pale green
  • lower leaves yellow and dead
• what's the use of magnesium in plants?

  • synthesis of chlorophyll which is needed for photosynthesis
• what are the symptoms of a magnesium deficiency?

  • chlorosis - due to less chlorophyll
  • stunted growth
• what's the use of potassium in plants?

  • production of flowers and fruit
• what are the symptoms of a potassium deficiency?

  • poor growth of flowers and fruit
  • yellow leaves
  • dead spots
• What are the physical defences of a plant?

  • cellulose wall not only provides support for the plant but also protection from microorganisms
  • the waxy cuticle of the leaf is a barrier to microbes from entering the plant, the only place they can enter is the stomata
  • bark provides a tough layer around the stem of the plant to prevent pathogens from entering
  • as deciduous trees lose leaves in the winter the infection can be taken with them
• what are the chemical defences in plants?

  • many plants produce chemicals which have antimicrobial properties
  • Many herbal face creams can use plant extracts such as tea tree oil, mint and witch hazel to have an antibacterial effect
  • More plants are being studied for their potential source of antibiotics as more strains are becoming resistant to current antibiotics
• Adaptations against herbivores

  • Herbivores eating a plant can seriously damage the plant structures and they will not flower and reproduce
  • Smaller insect infections can remove essential nutrients and energy from the plant and act as vectors for pathogens
• How does the adaptation of poison work and an example?

  • some plants produce poisons to deter herbivores from eating them, animals will quickly learn to avoid eating plants that will make them feel unwell
  • foxgloves, deadly nightshade and yew
• how does the adaptation of thorns work and an example?

  • make it unpleasant or painful for large herbivores to eat them
  • bramble, cacti and gorse
• how does the adaptation of hairy stems work and an example?

  • hairy stems or leaves deter insects and larger animals from feeding on them or laying eggs on the stem or leaves
  • poppies can be combined with poisons, nettles
• how does the adaptation of drooping or curling when touched work and an example?

  • this is a rare but effective mechanism, when touched the leaves will automatically curl which can dislodge insects and frighten off larger species
  • mimosa pudica will curl and point leaves to the ground when an insect touches it
• how does the adaptation of mimicry work and an example?

  • plants can droop to look as though they are diseased and trick animals into not eating them, they can also resemble larger insects to scare away any potential threats
  • passion flowers have evolved to mimic having butterfly eggs on its leaves so that butterflies do not lay their eggs, white deadnettle doesn't sting but it looks very similar to a stinging nettle