Researchers have solved the genetic code of the plant pathogen that caused the Irish potato famine over 100 years ago, revealing a blight genome that’s nearly “animal sized” and full of extra DNA that helps it decimate any defence put on by the host plant. “The genome is much larger than some of its relatives. The reason is it is full of these jumping genes that copy themselves,” says Chad Nusbaum of the Broad Institute of Massachusetts Institute of Technology and Harvard. This could explain how it attacked even potatoes genetically bred to resist this infection. Spread by spores, the disease is still a threat to global food security: in the U.S., for example, it kills tomato and potato plants on commercial and organic farms, causing large mold-ringed, green or brown spots on leaves, and blackened stems. It can wipe out a crop within days. The blight genome is 2.5 times larger than those of two relatives: P. sojae (which infects soybeans) and P. ramorum (which causes sudden oak death in trees). The blight genome has two regions, one full of copies of DNA that change rapidly; the other with a handful of genes, preserved over millions of years, that help infect the plant. This seems to allow for the rapid creation of hundreds of “attack genes” that evolve faster than the host plant, although it could take years more to figure out what these genes do.