Following completion of the study, the researchers looked through historical catalogues of large commercial nurseries in Italy and France and found records of mature Monterey cypress trees for sale during the late 1920s and 1930s, indicating significant imports of the California trees and their seeds at that time.
"It is very likely that the pathogen was introduced during that period," said Danti, who added that interviews the research team conducted with people who worked in the nurseries then suggested that cypress canker disease was becoming a problem by the late 1930s.
The researchers found three progenitor strains of the pathogen only in Tuscany, indicating that the disease was brewing there for several generations before exploding beyond the region's borders.
"It could have easily taken 10 to 20 years from the time of introduction for the first major outbreak to occur," said Garbelotto. "In Italy, the pathogen was first identified in 1951, so it could have arrived decades earlier."
The study authors advocate the genetic screening of plants to stem the spread of the disease, just as plant shipments in and out of California are now tested for the Sudden Oak Death pathogen.
"We can develop tests to screen for the presence of S. cardinale on plants that are traded, and even to test for the presence of strains that are currently not present in Europe or in the Southern Hemisphere," said Garbelotto. "Technological advancements of the last few years allow for the easy development of such tests, but it was essential to figure out the source of the pathogen in order to know what to look for."
Garbelotto said that researchers in Europe have spent the past three decades developing cypress trees that
|Contact: Sarah Yang|
University of California - Berkeley