Research

Phytophthora

Disease symptoms

Phytophthora is a genus which contains many important plant pathogens. Species can attack plants at or below ground level, causing crown and root rots. Phytophthora is spread by water, or in contaminated soil. Yew is particularly susceptible. Plants susceptible to Phytophthora - click here

The best known disease caused by Phytophthora is potato blight. This is one of the few species of Phytophthora which is wid dispersed and can attack the leaves.

The symptoms of Phytophthora infection include:

• Root and crown rots
• Aerial die-back
• V-shaped lesion often seen on one side of the trunk of trees or shrubs.

Phytophthora and its relatives

Pythium, Phytophthora and downy mildews are related and successively more specialised. They are more closely related to algae, rather than fungi. Pythium is largely saprophytic, whereas Phytophthora is a pathogen, parasitic on plants.

Testing for Phytophthora

The presence of Phytophthora in plant tissue is difficult to confirm. The fungus has to be baited out of the affected plant tissue or soil. This involves growing the fungus into apples and then plating onto selective media to induce sporulation. The Members Advisory Service carries out increasing numbers of baiting tests for Phytophthora in response to members' enquiries and these tests reveal that these pathogens are among the most frequent causes of plant death in gardens, particularly of woody plants. Currently tests take several weeks to complete. 20-30% of about 300 tests carried out per year are positive.

The Pathology research programme includes investigation of new techniques to speed up Phytophthora testing, such as molecular techiques incorporating the polymerase chain reaction (PCR). Other immunological methods have been considered but are not genus specific and are costly.

Techniques used for detection of presence of Phytophthora

• Apple baiting
• Direct plating on P10 or P5ARP
• PCR-based techniques based on ITS, cytochrome oxidase or elicitor genes

Phytophthora species found in garden plants

Plants show considerable variation in their susceptibility to Phytophthora infection. The aim of this project is to improve our knowledge of the identities of Phytophthora species occurring in UK gardens so that advice about control and less susceptible replacement plants can be given.

Techniques used for identification of Phytophthora species

• Morphological characteristics
• Molecular techniques including RFLPs and ITS sequencing

DNA was amplified from infected holly using primers ITS4/DC6 in the first round and ITS4/ITS6 in the second round followed by digestion with MspI.

The restriction pattern is specific to Phytophthora ilicis.

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