Mapping the Distribution of Phytophthoras in Britain

Phytophthoras are a group of microscopic fungal pathogens responsible for major plant diseases in many parts of the world, although prior to the 1990s they had relatively little impact in European woodlands. However, over the past two decades this has changed markedly and our aim is to improve understanding of the distribution of Phytophthora species in Britain and the trees they affect.

Research objectives

This project aims to analyse past and current records generated from various Forest Research projects and the Tree Health Diagnostic & Advisory Service to plot the distribution of the most damaging and best known species in Britain.

Specific objectives are to:

• Build spatial maps showing the distribution of a range of Phytophthora species.
• Show the host range of each mapped Phytophthora species, indicating the most common and least common tree hosts.
• Use the records, behavioral traits of each Phytophthora, and climatic data to predict how distribution may change in the future.

Results so far

Over 3,000 Forest Research records for Phytophthoras which date from 1975 to the present day have been analysed as a precursor to mapping. First draft distribution maps have now been generated for ten Phytophthora species frequently encountered in Britain. These are:

• Phytophthora alni
• Phytophthora austrocedri
• Phytophthora cactorum
• Phytophthora cambivora
• Phytophthora cinnamomi
• Phytophthora citricola (species complex)
• Phytophthora gonapodyides
• Phytophthora ilicis
• Phytophthora kernoviae
• Phytophthora pseudosyringae
• Phytophthora syringae

More recently, other less well known Phytophthora species including P. siskiyouensis, P. foliorum and P. gallica have also been found in Britain and research is underway to learn more about their behaviour and potential hosts.

Status

This project started the 1^st April 2015 and is ongoing

Contact

Joan Webber

Funders and partners

This project is funded jointly through Horizon 2020 and the Forestry Commission as part of the research programme Understanding Threats to Resilience

The research is in line with support to government policies of sustainable forest management as laid out in The UK Forestry Standard and its supporting series of Guidelines.

Phytophthora cinnamomi

This species, although an introduction, has probably been in Britain for more than 100 years. Although it is often found on ornamentals including shrubs, increasingly it has been found to affect trees such as sweet chestnut and oak, attacking the roots and root collar. The disease it causes on sweet chestnut is known as ink disease because of the blackish colour of infected roots and associated soil.

Phytophthora cinnamomi is favoured in continental climates, so is most frequently found in south east England. It is considered sensitive to frost, but despite this there are records of this species as far north as Scotland.

Tree genera affected by P. cinnamomi

Distribution map (2017)

Phytophthora citricola complex

This species of Phytophthora is widespread and based on dated records has been present in Britain for more than 80 years. In the early part of this century, P. citricola was found to be a complex of several morphologically similar species which have since been given different names. However, the species within the P. citricola complex which is most commonly identified in Britain is now calledP. plurivora. Most of the historic records of P. citricola are therefore likely to be P. plurivora.

Like P. cinnamomi, P. plurivora is a root attacking Phytophthora. It tends to grow best at higher temperatures and therefore is found most frequently in southern Britain.

Tree genera affected by P. citricola complex

Distribution map (2017)

Phytophthora pseudosyringae

This species was named as one of the newly defined species within the P. citricola complex in 2003, but has probably been present in Britain for decades and may even be a native. It has a much lower temperature optimum for growth compared with its ‘sister’ species P. plurivora.

Also like P. plurivora it often attacks the roots and root collar of beech, but it can also infect the aerial parts of trees. Phytophthora pseudosyringae has proved to be a very damaging pathogen to Nothofagus trees, particularly Nothofagus obliqua, causing trunk and branch lesions on this tree species and sporulating abundantly on the leaves. Its distribution in Britain is similar that of P. ramorum and it is found throughout much of western Britain.

Tree genera affected by P. pseudosyringae

Distribution map (2017)