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

Plant pathogens

• Plants can be infected with a range of viral, bacterial and fungal pathogens, such as:

  • tobacco mosaic virus (TMV)

  • rose black spot fungus

• Plants can also be infested with insects such as aphids, which can infest a plant in large numbers and feed on phloem sap, weakening the plant

  • Aphids can also act as a vector for the transfer of plant disease

Detecting plant diseases

Higher Tier Only

• Detecting and identifying a disease allows effective treatment to be provided

• Plant disease is usually detected by observing visible symptoms:

Identifying plant diseases

Higher Tier Only

• There is some overlap between the symptoms of different plant diseases, making disease identification challenging; methods of identification include:

  • comparing symptoms to those described in gardening manuals or online

  • experts visiting an agricultural field or woodland to collect samples for identification in a lab

  • testing kits which contain monoclonal antibodies to identify the presence of pathogens quickly and easily

Mineral deficiencies

• Plant growth can also be affected by mineral deficiencies

• Plants may deficient in:

  • nitrates

  • magnesium

Nitrates

• Used in production of amino acids for proteins

• Symptoms of deficiency include:

  • stunted growth

  • upper leaves pale green

  • lower leaves yellow and dead

Magnesium

• Used in synthesis of chlorophyll. Less chlorophyll means less light is absorbed, so the rate of photosynthesis is lower, so less glucose is made for growth (e.g. less glucose converted into protein), so growth is stunted

• Symptoms of deficiency include:

  • yellowing leaves (chlorosis) due to a lack of chlorophyll

  • stunted growth.