Scientists lay bare Irish potato famine blight

Scientists have successfully sequenced the genome of Phytophthora infestans - the potato blight mould which in the 1840s devasted Irish potato crops, leading to the deaths of one million people.

According to Nature, Phytophthora infestans is a water mould (oomycete) which "causes late blight in potatoes, consumes and rots the leaves and tubers of the plant". It adds: "The mould still afflicts potatoes, tomatoes and related plants, and costs farmers around the world an estimated $6.7bn a year."

Now, though, an international team has "identified a number of genes that might be responsible for the blight's destructive powers - and keys to its undoing".

The researchers discovered that parts of the "unusually large" genome "stood out as being highly variable", or full of "transposons", described as "sequences that make copies of themselves and jump around in the genome". The scientists believe the transposons - comprising a whopping 74 per cent of the genome - allow the mould to quickly evolve to defeat genetic countermeasures intended to stop it in its tracks.

Potato breeder John Bradshaw, of the Scottish Crop Research Institute (SCRI) in Dundee, explained: "At the moment, the breeding strategy has been based on screening the wild relatives [of the potato] from the highlands of Mexico and parts of the Andes such as Bolivia that have resistance."

However, Bradshaw noted: "What has happened is after taking 15 years to incorporate this resistance in a cultivar, it would take Phytophthora infestans only a couple of years to defeat it."

Scientists now hope to pinpoint those Phytophthora infestans genes which are "absolutely required for late blight disease development", as Dr Stephen Whisson of the SCRI put it to the BBC.

He added: "The products from these essential 'disease' genes are then potentially useful to target for resistance in potato breeding programmes, or in development of more specific and environmentally friendly control chemicals."

Bradshaw concluded: "With all this knowledge about how the pathogen attacks the host on the biochemical level, I would hope that some clever plant pathologist would be able to genetically engineer resistance." ®