Detecting and identifying plant diseasesSpec 5.11B
In short
Plant diseases are detected and identified in four ways. Environmental causes, such as a mineral deficiency, are eliminated. Distribution analysis maps affected plants to see whether a pathogen is spreading. Visible symptoms, such as spots or wilting, are compared with known diseases. Diagnostic testing, for example using antibodies or DNA tests, identifies the pathogen.
Plant diseases can be detected and identified in the field and in the laboratory. There are four approaches you need to be able to describe.
| Method | What is done | What it tells you |
|---|---|---|
| Eliminating environmental causes | Check conditions such as soil nutrients, water supply, temperature and pollution | Whether the symptoms could be caused by something other than a pathogen, such as a mineral deficiency or drought |
| Distribution analysis | Record where affected plants are, for example on a map | Whether the pattern points to spread of a pathogen (clusters around a source) or to an environmental cause (an area with poor soil) |
| Observing visible symptoms | Look for spots, discolouration, lesions, wilting, growths or leaf loss | Which disease it is likely to be, by comparing with known examples |
| Diagnostic testing | Test samples in the laboratory, or use testing kits in the field, for example kits that use antibodies to detect a pathogen's antigens, or tests that identify its DNA | Which pathogen is present |
Visible symptoms alone may not be enough, because different problems can look similar. For example, yellow leaves can be caused by a mineral deficiency or by a pathogen. That is why environmental causes are eliminated first and laboratory tests are used to confirm the pathogen.
In a 'suggest how' question, combine two methods: use distribution analysis to see if the disease is spreading, then diagnostic testing to identify the pathogen.
Quick check
Name two physical barriers that protect plants from pathogens.
Show answer
The leaf cuticle and the cell wall.
Give one way plant chemicals can be useful to humans.
Show answer
Some can be used as medicines to treat disease or relieve symptoms, for example aspirin from willow.
Why do scientists eliminate environmental causes when investigating a plant disease?
Show answer
To check that the symptoms are not caused by something such as a mineral deficiency, rather than a pathogen.
What is distribution analysis?
Show answer
Recording where the affected plants are to look for a pattern that suggests the cause.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026