Scientists blamed the wrong fungus for the potato blight which caused the Irish Famine, according to the journal Nature. More than a million people died in the Famine between 1845 and 1850 and another million emigrated.
US researchers found that DNA taken from potato leaves preserved from the Famine showed no signs of the strain of the organism scientists blamed for the crop failure. The DNA tests identified three other strains of the pathogen Phytophthora infestans which had not been considered before.
"The theory was that the 1b haplotype was the strain that had caused the Famine, but that work was all based on studies of modern, 20thcentury DNA from modern isolates [samples]", said Dr Jean Beagle Ristaino, a plant pathologist at North Carolina State University.
Dr Ristaino's team was the first to use potato leaf specimens dating from 1845/47. "Our work refutes the modern-day work", she said.
The research has important present-day implications, because the pathogen which caused the Famine is still a threat in many developing countries, and new strains are resistant to pesticides.