New SOD Strain Enters Into the U.S.

January 28, 2005 - 12:25

“A previously unknown strain of the tree-killing disease Phytophthora ramorum, more commonly as sudden oak death (SOD), has been found in a nursery in Washington state, a possible mutant child of the fast-spreading pathogen,” asserted a recent article in the San Francisco Chronicle.

According to the article, this new strain is a combination of two different types of Phytophthora: the version that we have here in the United States and a more aggressive version from Europe. The article states that this new strain may possibly be the offspring of the two versions mixing together; however, at this point, scientists have not been able to officially prove that as the case.

“‘We detected a third strain with traits from both the U.S. and European strains," said UC Berkeley forest pathologist Matteo Garbelotto during a three-day Sudden Oak Death Science Symposium in Monterey. "It has some genetic traits in the DNA that we've never seen. It's a unique strain.’” stated in the article.

“‘The obvious risk," said Jonathan Jones, who manages the sudden oak death program for the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, "is that there could be sexual recombination, and we could end up with something worse than what we have,”’ the Chronicle continued.

Despite the new findings, the Chronicle said that Garbelotto, who helped discover Phytophthora ramorum feels that at this time people should not be extremely excited about the new strain because, “it has ‘not been particularly aggressive on oaks.’”

According to the Chronicle, the new strain was found this past summer on a plant in a nursery where both the American and European strains were known to exist. Though different strains, this is the equivalent of a male and female of the same species and may have led to the intermingling.

“The European strain has been deadly to England's ubiquitous rhododendrons and beech trees, but it wasn't until 2003 that it was detected in a nursery in British Columbia. It has since been found in nurseries in Oregon and Washington,” according to the article.
“‘One hypothesis is that it is the result of recombination," Garbelotto said. "The other hypothesis is that it's a representative of the species that predates the split between the European and U.S. mating types and it was introduced separately. It's interesting because it offers us another clue into the origin of this Phytophthora species. Maybe we can find out where this plant came from and trace the disease back,’” stated the Chronicle.

According to the article, “Scientists have long suspected that the pathogen was an exotic species introduced to America and Europe from some far off place, most likely Southeast Asia. Genetic evidence collected as a result of the sequencing last year of the P. ramorum genome, supports that theory. In fact, said Garbelotto, the California outbreak appears to have come from a single alien microbe that hitched a ride to the Golden State, cloned itself millions of times and then did its dirty work.”

In addition to this new strain emerging here in the states, ANLA is reporting a new form of Phytophthora has been found in England. The current proposed name is Phytophthora kernovii. According to the ANLA Update, this new pathogen seems to be much more aggressive than Phytophthora ramorum and also seems to have a broader host range. “Some English scientists suspect that the disease may have come from China on magnolia,” said the Update. ANLA is recommending that U.S. nurseries importing plant material from Europe or Asia should be very careful and check for signs of disease right away.
According to the Chronicle, "The disease itself seems to be progressing more rapidly than ramorum," said Stephen Hunter, head of plant health for the Department for Environmental Food and Rural Affairs in Britain. "There is a lot of concern."

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