Comparison of techniques for the detection of Phytophthora

RHS project team

Dr. Geoff Denton

Partners

Dr. Simon Archer, Imperial College

Start date

01/01/2006 11:00:33

End date

31/12/2014 11:00:43

The problem

Phytophthora species are only visible with the aid of a microscope. Plants react to infections with discolouration of the plant tissue and in the case of Phytophthora this can cause foliar lesions, bleeding cankers, stem lesions and blackening of roots. These plant symptoms can be caused by other diseases, pests or stresses on the plant. Detection and confirmation of the correct causal agent is paramount to being able to provide useful advice.

Detection and confirmation of Phytophthora species in samples received through the RHS Advisory Service has traditionally relied on trying to grow a live culture of the pathogen. Many molecular techniques have been developed, able to detect Phytophthora proteins or DNA directly within plant and soil samples. Research has shown these molecular techniques can detect as little as 1 to 100fg (femtograms) of DNA. One fg is equal to 0.000000000000001g, as an example a single grain of table salt weighs approximately 100 billion femtograms.

Although these new methods are highly sensitive, before changing our current system we need to confirm that they are as reliable as our existing measures. The new methods need to be able to detect any Phytophthora species from any host plant. This is a huge challenge as there are around 100 Phytophthora species recorded and there are around 23,000 taxa of plants (within 1,616 genera) in RHS Garden Wisley alone. This gives some illustration of the number of possible hosts that we can see.

By comparing various techniques for the detection of Phytophthora species from RHS Advisory Service samples we can improve detection and give clearer advice.

Approach

Samples received through the RHS advisory service showing typical Phytophthora symptoms are put forward for further testing. These samples are processed using three detection methods:

• Recovering a live culture of Phytophthora, using a fruit as a bait. Once a live culture is recovered, production of spore-containing structures (sporangia) is required for positive identification.
• Detection of Phytophthora using nested PCR. Regions of DNA have been shown to have specificity to different genera/families. One of these has been chosen and if this region is detected then it is recorded as a positive result.
• Detection of Phytophthora using antibodies. Commercial tests are available with embedded antibodies for the detection of Phytophthora. One of these has been chosen and the production of an appropriate band was recorded as a positive results.

Benefits to gardeners

This project will compare methods for detection of Phytophthora species in plant and soil samples. Improved detection will provide gardeners with a rapid and accurate diagnosis and enable specific advice to be given by the RHS Advisory Service. This will help with the detection of this increasingly important pathogen of garden plants.

Further information

Detection and diversity of phytophthora in UK gardens poster (2MB pdf)

Phytophthora survey

Pythium, a garden pathogen?

Advisory information

Phytophthora root rot

Phytophthora ramorum and P. kernoviae