Strains of the disease that caused the Great Famine in Ireland have been traced to tomato crops in the Salinas Valley in California, researchers have found. "It's still a problem today," said Frank Martin, a Salinas native and plant pathologist at the USDA. "It hasn't gone away."
Although the Irish strain has since died out, both potato or late blight and tomato blight are caused by a fungus-like, single-celled microbe called Phytophthora infestans
, which thrives in wet environments and produces long-lived spores that travel in the wind.
Wayne Gularte, a tomato farmer for Rincon Farms in Gonzales, said that he lost about half of his crop this year to tomato blight. Just a little rain or fog can create the perfect environment for an outbreak. Gularte says there are preventative sprays that protect the fruit before it rains, but once the blight sets in, there is nothing a farmer can do to save the crop.
Scientists believe the disease originated in Toluca Valley, Mexico. It traveled through the U.S. in the 1800s and then jumped across the Atlantic Ocean to Europe in 1845. The organism that caused the Great Famine was a pandemic strain that spread throughout Europe and went extinct after potato breeding programs developed a tuber resistant to the organism.
The origin of modern strains is still unclear to researchers, although they do believe they also came from the U.S. and then spread to Africa, Asia and South America. About 120 different species of Phytophthora
exist. Farmers lose over $6 billion a year in damaged crops and fungicide costs, and tomato growers in the Salinas Valley feel the effects of the blight keenly.
Martin is currently working on developing tests that will rapidly detect P. infestans
, as well as other related organisms that cause plant diseases worldwide.