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GENETIC fingerprinting has overturned theories about the origins of the
fungus that caused the Irish potato famine in the 19th century. The work could
help botanists find naturally resistant potato strains.

When the fungus Phytophthora infestans appeared in Ireland in 1842,
it destroyed the potato crop and caused more than a million people to starve to
death. A similar fungus still causes 鈥渓ate blight鈥� in potatoes, and everyone
assumed that this modern strain, called 1b, is directly descended from the one
that devastated Ireland.

Now Jean Ristaino at North Carolina State University in Raleigh has compared
the DNA of the modern fungus with 150-year-old samples stored at the Royal
Botanic Gardens in Kew. They have done some remarkable 鈥渕olecular archaeology鈥�,
says Nicholas Money, a mycologist at Miami University in Oxford, Ohio. 鈥淭hey
went back to samples taken by some of the leading plant pathologists of the
诲补测.鈥�

Ristaino discovered that the old Irish strain is missing a sequence found in
all samples of 1b. That means modern late blight is not directly descended from
the Irish blight. What鈥檚 more, it knocks a hole in the theory that modern blight
originates in Mexico.

Mexico has more strains of P. infestens than anywhere else鈥攂ut
not the 1b strain. So modern blight must have come from somewhere else, perhaps
in South America. If its area of origin can be found, this would be the best
place to look for potato strains with natural resistance.

Money says the work shows the importance of herbariums like Kew鈥檚 at a time
when many are losing funding.