Pythium, a garden pathogen?

RHS project team
Dr. Geoff Denton
Dr. Simon Archer, Imperial College
Start date
29/01/2008 14:26:00
End date
29/12/2014 14:26:04

Phytophthora, Pythium, survey, pathogen, pathogenicity, UK gardens, RHS Advisory Service, damping off

The problem

The RHS researches Phytophthora, a known plant pathogen with a wide host range, of which there are around 100 known species. Pythium, closely related to Phytophthora, has more than 150 species recorded, but they are not all plant pathogens like Phytophthora species. Some are free living in the soil and water, whereas others are pathogenic with Pythium species known to infect animals, fungi and plants.

Through the Phytophthora research, large numbers of Pythium species have been identified coming from dead or dying plants and in the absence of other pathogenic fungi. Much is written about Pythium species involvement in damping off of seedlings and causing damage to commercial plants via irrigation systems.

This study will investigate the pathogenicity of Pythium species towards mature plants and their prevalence within UK gardens.


To understand the diversity of Pythium species within UK gardens a survey was initiated. Symptoms caused by Pythium species are similar to those caused by Phytophthora species. So plants received through the RHS Advisory Service with typical indications of a Phytophthora infection, foliar dieback, stem lesions or blackening of the roots, were additionally tested for the presence of any Pythium species.

The detection methods for Pythium species from samples received through the RHS Advisory Service were;

Detection using nested PCR. Detection of a specific region of Pythium DNA followed by identification through sequencing

Recovering a live culture of Pythium, using seeds as a bait. Live cultures are recovered and identified through sequencing the Pythium DNA

Culture, or isolates, will then to be used to inoculate host plant to check aggressiveness.

Benefits to gardeners

This project is to evaluate the possible impact to gardens and garden plants from the presence of Pythium species.

As more new Phytophthora species are being identified as major pathogens of ornamental plants the impact of the closely related genus Pythium within gardens is relatively unknown. Our research will benefit gardeners by establishing the diversity of Pythium species and potential to cause major damage to ornamental plants.

Summary of results

The preliminary results have identified over 25 named Pythium species in UK gardens, with several putative new species also identified. Over the four year study, confirmed Pythium cases were associated with 90 host families encompassing 175 genera. The top host plant record was Taxus, and was associated with 17 named Pythium species.With the top Pythium species identified being Pythium intermedium, Pythium attrantheridium and Pythium sylvaticum.

Although a wide diversity of Pythium species were detected, the majority being identified are known pathogens of plants, and records have them associated with damage to seedlings. Further work will also look at improving our methods for identification to species level.

Preliminary results from investigations into the pathogenicity of Pythium species have demonstrated that Pythium is able to kill woody plants. In addition, Pythium species were also found to be able to foliar blights on mature, woody plants.

Further information

Phytophthora survey

Advisory information

Phytophthora root rot
Phytophthora bleeding canker
Advice on damping off
Phytophthora ramorum and P. kernoviae

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.