Mystery Oak Disease pg.4
It was a brand new species of Phytophthora, never before identified, airborne and aggressive, with no known natural enemies. “For the first time we have an organism that can infect a broad host range of plants in this country, with a biology that’s completely unknown,” says Matteo Garbelotto, a forest pathologist at the University of California-Berkeley. “It’s like all of a sudden finding a very poisonous snake that can fly.”
Garbelotto and another scientist, David Rizzo at the University of California-Davis, are the first to use DNA technology on a new forest disease. They isolated Phytophthora ramorum’s DNA, tested hundreds of samples for its presence and identified 14 hosts in just 18 months, a process that would have taken years under conventional plant-pathology methods. More hosts are likely to be identified.
They’ve probably slowed Sudden Oak Death’s spread because their findings allow state and federal regulators to act quickly to ban movement of additional host plants from nurseries. The scientists have asked the U.S. Energy Department to fund gene mapping of the pathogen.
But what eludes them is a cure. In the lab they’re studying organic chemicals, biological compounds that might prevent infection by Phytophthora spores. They’re testing different types of protective trunk coatings that could be applied to a tree. They’re also trying to develop ways to boost a tree’s own defensive response. But nothing yet has proved a magic bullet. Another option is simply removing host species like bay laurel from the forests, but that could have unknown effects on an ecosystem.
Knowing where Phytophthora ramorum came from would help, but that, too, remains a mystery. It could be an exotic organism, accidentally introduced from a locale where native plants have resistance to it. Once here, it feasts on hosts that have no defense. It could be a new species produced by genetic change, a hybrid with a potent effect on oaks. Or it could have been present all along, benign until an unknown factor caused it to become destructive.
Some speculate that several wetter-than-normal winters are linked to the emergence of Sudden Oak Death. The pathogen is a fungus-like organism similar to algae that thrives in moist conditions. Others think pollution is a culprit, but Garbelotto discounts that. He says environmental factors could have sparked change in the pathogen, but he sees little evidence that they weakened the oaks.
