THE blight that triggered the great famine in Ireland in 1845 is still the biggest disease threat to spuds worldwide 鈥� and it鈥檚 no wonder.
Researchers have sequenced the genome of the mould that causes blight and found it keeps a huge arsenal of potato-destroying genes, ready to evolve around whatever defences taters can muster. On the plus side, the sequence also suggests ways to fight back.
Blight is caused by an oomycete or water mould, Phytophthora infestans, related to brown algae. Sophien Kamoun of the Sainsbury Laboratory in Norwich, UK, and colleagues report that P. infestans has a genome three times as large as its closest relatives, because it keeps many different variants of its 鈥渁ttack鈥� genes (Nature, ). These code for enzymes that kill potato cells, on which the mould then feasts. There are numerous variations, with many bits of DNA that jump around the genome, allowing the continual generation of more variation. This means the blight can make new enzymes as fast as potatoes evolve ways to neutralise the old ones.
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However, the team also found virulence genes in regions of the genome that are not so variable. 鈥淭hose could be great targets for plant resistance,鈥� Kamoun says.
