Detection and Identification of Plant Diseases (AQA GCSE Biology): Revision Note

Plant pathogens

• Plants can be infected with a range of bacterial and viral pathogens; such as the tobacco mosaic virus (TMV) and rose black spot fungus (see Viral Diseases and Fungal Diseases)

• Plants can also be infested with insects such as aphids

  • Aphids have 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 also 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

Detecting plant diseases

Higher Tier Only

• Infections in plants as with all organisms are better when detected and treated quickly

• Symptoms of diseases in plants include:

Plant diseases table

Identifying plant diseases

Higher Tier Only

• 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

  • For crop plants or forest trees, experts may visit the field or woodland to take samples which used for pathogen DNA analysis in a laboratory

  • Plant scientists, foresters, farmers and market gardeners can use testing kits which contain monoclonal antibodies to identify the presence of pathogens quickly and easily

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

Nitrates

• Use in the plant: Production of amino acids for proteins.

• Symptoms of deficiency: Stunted growth, upper leaves pale green and lower leaves yellow and dead.

Magnesium

• Use in the plant: Synthesis of chlorophyll. Chlorophyll is needed for photosynthesis.

• Symptoms of deficiency: Yellowing leaves (chlorosis), due to less chlorophyll and stunted growth.

Potassium

• Use in the plant: Production of flowers and fruit.

• Symptoms of deficiency: Poor growth of flowers and fruit, yellow leaves and dead spots.