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From: Rhodo Group Main Page: http://www.egroups.com/group/rhodo http://www.berkeley.edu/news/media/releases/2001/01/10_oak.html UC researchers announce results that could complicate measures to halt spread of Sudden Oak Death 10 Jan 2001 By Catherine Zandonella, Media Relations Berkeley - A common nursery plant may lead to increased complications and possible new management practices in the fight to halt Sudden Oak Death, a highly contagious fungal disease that is killing California oak trees, University of California researchers announced today (Wednesday, Jan.10). In a breakthrough in the study of the disease, UC researchers discovered that the rhododendron, a popular ornamental plant, can be infected by the same fungus that is causing the oak disease. The fungus has infected European rhododendrons and, as of yesterday, the researchers confirmed that it also is affecting California rhododendrons, suggesting a transcontinental link. Finding this relatively new fungus in two different parts of the world - and in two species - is unusual, the researchers said. The rhododendron discovery gives insight to the potential origin and transmission of this pathogen and may suggest new ways of spread. Previously, the pathogen only was known in three other California oaks - tanoaks, coast live oaks and black oaks. "We now know we have a host that could have carried the fungus a long way," said Matteo Garbelotto, a plant pathologist and adjunct professor in the Department of Environmental Science, Policy & Management in UC Berkeley's College of Natural Resources. "People don't really export oak trees across state lines or around the world," he said, "but they export rhododendrons." The finding may have a major impact on how scientists manage the disease. Co-investigator David Rizzo, assistant professor of plant pathology at UC Davis, said it may result in new restrictions on the rhododendron nursery industry. "The big concern is that someone will transport a sick rhododendron to a place where there are susceptible oak species," he said. The breakthrough came when a Clive Brasier, British researcher who had visited UC Berkeley last summer, later noticed in Europe a fungus that looked like one he'd seen in Garbelotto's lab. The European fungus had been found on rhododendrons in Germany and the Netherlands. Brasier contacted the UC scientists, and researchers from all four countries determined together that the European rhododendron fungus was identical to the California oak-killing agent. This finding established that the fungus is not exclusively found in California and has important implications for international trade. But Rizzo and Garbelotto needed more proof to confirm the link between the two plant species, and yesterday they got it. Rizzo and Steve Tjosvold, a Santa Cruz County farm advisor, found the fungus in a rhododendron taken from a Santa Cruz County nursery, and Garbelotto confirmed with DNA analysis that it was the same fungus killing the oaks. The scientists don't know whether the disease was transmitted from California to Europe, or vice versa, or whether it traveled to both places from a third, as yet unknown, location. The fungus, first noted in European rhododendrons in 1993, has not been found in European oaks. However, European scientists are concerned that the disease will spread to European oak forests, particularly those in areas with a climate similar to that of California. Since the discovery of the mysterious oak-killing illness in California in 1995, researchers have been scrambling to understand the disease and design strategies to stop its spread. It is not known if the fungus recently was introduced into California, or if it is a native fungus that recently became a tree-killer because of environmental changes. Tens of thousands of oak trees have succumbed to the disease, and the researchers have reported up to 80 percent mortality in some infected groves. Through molecular sleuthing, Rizzo and Garbelotto determined that the disease was caused by a never-before-seen strain of fungi from the genus Phytophthora (Phy-TOFF-thoruh). A relative belonging to this 60-member group caused the Irish potato famine, and another relative is linked to the dieback of cedar trees in Northern California and southern Oregon, eucalyptus trees in Australia and oaks in Mexico, Spain and Portugal. In California, Sudden Oak Death has been reported from Sonoma Valley in the north to Big Sur in the south, a 190-mile range, as well as east to the Napa County border, about 25 miles inland. The hardest hit counties are Marin and Santa Cruz. The disease affects tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), and California black oak (Quercus kelloggii) found along the coastal belt in California. To date, the disease has not been found in other oaks such as blue oak or interior live oak. The dieback is alarming, researchers say, for its potential to disrupt the coastal forest ecosystems. Oaks provide habitat for wildlife and a food supply for small mammals and are frequently planted as ornamentals in gardens and parks. Additionally, downed dead trees create a fire hazard from the resulting buildup of dry fuel. There are similarities between the disease in oaks in California and rhododendron in Europe. In both cases, the fungus attacks above ground parts of the plants. In oaks, the fungus enters through the trunk and causes the formation of bleeding cankers on the trunk. On rhododendron plants, the fungus causes similar cankers and spreads from twig tips to the stem base, according to the European researchers. The researchers have notified agricultural and ecosystem managers in the affected areas of the rhododendron discovery. Research is underway to determine if native rhododendrons - those that have not been imported - are being infected. Research also is being conducted to determine how many other susceptible species may be affected by the fungus. *************************** Dr. Andrew J. Storer Division of Insect Biology 201 Wellman Hall University of California Berkeley, CA 94720-3112 USA Tel: (510) 642 5806 Fax: (510) 642 7428 email storer@nature.berkeley.edu ----------------------------------------------------------------- There is further information regarding topic at http://camfer.cnr.berkeley.edu/oaks/ Margaret ------------------------------------------------ From what I understand from the information available is that it appears to be almost totally destroying the 3 species of oak named in the report that are native to California. So far, European oaks have not contracted it, but rhododendrons in both California and Europe have been infected with it. It is a relatively new fungus. It would appear that the rhododendron is the host plant, given that oak trees aren't exported. The same (exact same DNA) Phytophthora has been known in European rhododendrons since 1993 but is not the same as other Phytophthora strains that also affect rhododendrons. The mystery is, where did it originate? ..... if it didn't come from Europe via rhododendrons shipped to California, did it travel to Europe from California? Or is there a third locale, such as rhododendron collections from Asia? Perhaps there is another host species which is contaminating both rhododendrons and oaks. Perhaps it is a native fungus that went through a mutation due to environmental changes or proximity of new host species. To answer your question, it does not seem to be a soil-borne fungus as it attacks above-ground parts of both plants: in oaks, through the trunk causing bleeding cankers on the trunk; in rhododendrons it causes similar cankers and spreads from twig tips to the stem base. There is more information at other sites - will find the links again. Diana Pertson --- Jan 2002 I have been following this since it was first reported and communicated with Dr. Storer to get info on its relation to rhododendrons so I could alert members of the ARS. In my opinion, the pathogen is a new discovery but may not be a new disease. There are many other diseases of oaks and rhododendrons. Oaks in particular have been suffering from these for a long time. Diane Pertson ------------------------------------ The following is from 'more background information' at: http://camfer.cnr.berkeley.edu/oaks/Rhododendron.html Clive Brasier ( Forest Research, Alice Holt Lodge, UK) has determined that a new species of Phytophthora isolated as early as 1993 from ornamental Rhododendrons in Germany and The Netherlands matches the newly-discovered species found in California. This new Phytophthora appears to be genetically distant to most of the other 60 species within the genus Phytophthora. The closest relative in the genus is Phytophthora lateralis, a virulent pathogen of Port Orford Cedar known to be present in natural stands of the Pacific North West and occasionally on Port Orford Cedar stock in nurseries in Europe. · The presence of the same pathogen in two discrete and extremely distant areas raises important issues on the potential mode of transfer of an aggressive pathogen between continents but provides no information on where the pathogen may have originated. The pathogen may have originated in either known areas of distribution or in a third region of the world. · In California, there is a substantial overlap between areas in which rhododendrons grow and areas in which the oak species known to be susceptible to the new disease are found. Rhododendrons are also extremely common ornamental species throughout the state. ---------------------------------------- The California report mentions that the spread may be from spores that are splashed by raindrops from the soil rather than airborne. In any case any source of spores, soil or diseased plants, would lead to spread. "The pathologists on the team have isolated an important causal agent - Phytophthora, and beetles, other fungi, and weather may be additional factors. Phytophthora is a fungus that appears to enter through the bark on tree trunks and limbs, possibly after they are splashed there by raindrops. Once in the tree, the fungus produces enzymes that dissolve the dead outer and living inner layers of bark. Oozing sores result as the cell walls break down. (from the UC Davis Press Release). Once the trees have gone through the progressive stages of the symptoms, their vigor rapidly declines and they become vulnerable to secondary insect pests such as bark and ambrosia beetles. Pseudopityophthorus (bark beetle) occupies the phloem-xylem portion of a tree, at the bark-sapwood interface, whereas ambrosia beetles bore deep into the heartwood of the tree, and kill it by blocking its circulatory system. These beetles are not known to be capable of invading healthy trees but can be very destructive if trees are weakened. As the number of dead and beetles-infested trees increases, this may provide a reservoir of colonizing beetles that can attack other weakened trees." Cheers, Steve Henning in Reading, PA USA ----------------- There was a previously unidentified phytophthora infection in rhododendrons in Germany and the Netherlands, first reported in 1993 . A botanist researcher at the University of California at Berkeley, noticed in late 2000 that it closely resembled the then unidentified fungus in California oaks. DNA tests then revealed that it was the same species of phytophthora. Any suggestion that it spread from California to Germany or vice versa is pure speculation at this point. It could have been around in another host plant for eons, and then moved into rhododendrons oaks, and later many other California species. DNA-wise, it is very closely related to Phytophthora lateralis which infects the Port Orford cedar in the US Pacific northwest. It is possible it mutated from that species. Its effects on rhododendrons has been observed here in California. It is not lethal to the plant, and may be treated (in rhododendrons) by application of fungicides (I don't remember which ones). A website with links to further information: http://cemarin.ucdavis.edu/index2.html Richard Starkeson ------------------------