Scientists at North Carolina State University have discovered that the fungus-like pathogen that caused the 1840s Irish potato famine originally came from the Andes of South America.
By comparing the sequences of both the nuclear and the cellular powerhouse, mitochondria, of nearly 100 pathogen samples from South America, Central America, North America and Europe, Dr. Jean Beagle Ristaino, professor of plant pathology at NC State, and a small team of researchers created "gene genealogies" that point the finger at an Andean point of origin for the pathogen, which is known as Phytophthora infestans.
The research is published online in Proceedings of the National Academy of Sciences.
Like family trees that genealogists use to trace family histories, the scientists used the pathogens' gene genealogy to track migration patterns of the different strains, or haplotypes, of the pathogen. In essence, Ristaino, former grad student Luis Gomez-Alpizar and Dr. Ignazio Carbone, all of NC State's Department of Plant Pathology, figured out how the pathogen's genes changed over time and tracked these changes on maps that look similar to family trees.
"By studying the pathogen's mutations, or changes in DNA, you can tell where the mutations originated and what strains spread to different parts of the world," Ristaino says. Most of the early mutations occurred in Peru and Ecuador in South America, according to the researchers' data.
Ristaino says there are a number of camps on the issue of the pathogen's center of origin. While 19th century scientists believed P. infestans came from South America, some present-day scientists believe Toluca, Mexico, to be the origination point. Early in the 20th century, Ristaino says, Toluca became a center for plant breeding studies, as scientists there collected potato seed from all over the world and tested it for resistance to the pathogen.