THE INCREDIBLY destructive water mould that transformed Irish history by triggering the potato famine has been exposed in all its remarkable complexity.
An international team of scientists this morning publishes the full genetic blueprint of Phytophthora infestans, the organism that helped kill a million people and drove a million more into exile.
The researchers from countries across the world including Ireland were taken aback by what its genome revealed, said Prof Sophien Kamoun, head of the Sainsbury Laboratory in Norwich. The organism has an exquisite system for genetically rearranging itself, making it exceptionally damaging to potato and tomato crops.
The same organism that triggered wholesale potato blight and subsequent famine in Ireland, called a fungus by many but in fact a water mould, continues to cause destruction. It wiped out the potato crop across Papua New Guinea in 2003 and causes blight losses worldwide worth more than €4.6 billion annually.
Prof Kamoun released details of the P infestans genome yesterday to media attending the annual British Festival of Science, which ends today. He and Prof Brian Haas of the Broad Institute of the Massachusetts Institute of Technology and Harvard University publish their findings this morning in the leading journal Nature.
The spore-producing mould has an awesome potential for virulence. The research shows it has what Prof Kamoun calls a “two speed” genome. There is a stable, unchanging part that takes care of normal “housekeeping” such as growth and spore formation but another that reforms readily to produce new genetic variants.
Unfortunately, this unstable area is where the organism gets the genes it needs for disease virulence. “There are regions in the genome where the genes are very tightly packed together, but there is another region where there are many [DNA] repeats and few genes. The genes that are important for virulence populate this repeat region.”
There are no fewer than 500 genes there and probably more, with the area of repeating DNA taking up a full three quarters of the total genome, Prof Kamoun said. This means the mould can reinvent itself again and again every time it reproduces, making attempts to control it difficult.
One recent manifestation of this is a new strain of P infestans called A2-Blue-13. First detected in the UK in Ipswich in 2005 when it accounted for 38 per cent of blight cases, it now represents 80 per cent of all blight and has spread right across Britain. It is also causing problems on Irish farms.
How unready Irish farmers in 1845 must have been for a disease that left a third of the then population unable to feed itself, given that all of the technology available to us today can still do little more than hold P infestans in check.
Yet having the genome in place opens up the possibility of new approaches to control it, Prof Kamoun said. The battle against this old enemy continues.
