In the mid-19th century, a fungus-like disease that turned potatoes into black, inedible mush led to the fatal starvation of approximately a million people in Ireland. A team of DNA sleuths now believes they know the true identity of the killer disease. The mystery began unraveling three years ago, when the researchers presented DNA evidence from samples of 150-year-old potato leaves. The scientists said the findings exonerated the previous prime suspect behind the Irish potato famine: a strain of the pathogen Phytophthora infestans known as the Ib haplotype. (The pathogen causes a plant disease known as late blight.)
