Furthermore, obtaining pure cultures of Phytophthora from such substrates is challenging as it tends to be slow growing on agar. The paucity of reliable markers makes species identification difficult and considerable morphological plasticity displayed within some taxa limits the utility of many identification keys. Sole reliance on morphological and physiological methods can result in mis-identification to the detriment of both practical control and clear scientific communication. In the past, new species have been wrongly assigned to current taxa and, conversely, morphological variants of existing taxa incorrectly assessed as new disease threats. Such misidentification, or isolates identified simply as 'unknown Phytophthora sp.' can delay the realisation of new threats and result in failure to offer suitable advice to growers.
Accurate identification is also crucial to plant health legislation and plant quarantine issues.
The true extent of diversity in the genus is unknown since, until recently, there had been no comparative studies using a methods which resolve at an appropriate taxonomic level. The organisation of Phytophthora DNA arrays and details of the PCR products utilised in this module are shown. In a robust, PCR-based assay involving the amplification of a 900 base pair amplicon and its digestion with a range of restriction enzymes a characteristic profile or fingerprint is produced. Such profiles are, almost invariably species-specific and a comparison against a reference collection offers rapid species identification. Such software is not available in all laboratories so this web site includes a database of ITS digest profiles of 46 Phytophthora species.