A VIRULENT new pathogen is attacking California鈥檚 giant redwoods and Douglas firs, which are among the tallest and most long-lived trees in the world.
The appearance of the fungus-like alga, called Phytophthora ramorum, threatens California鈥檚 $3 billion timber industry. The two species account for half the timber harvested in the state each year.
Researchers at the Davis and Berkeley campuses of the University of California announced last week that they had found the pathogen infecting coast redwoods and Douglas firs in several Californian locations. They have also managed to infect cuttings of the trees in the lab.
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Experts are not sure what impact the alga will have on the trees. The disease attacks their foliage, but hasn鈥檛 done serious damage so far. On the other hand, it may simply take time to kill the large trees.
P. ramorum was discovered in California in 1995 and dubbed sudden oak death disease. While some trees infected by the alga, such as the California buckeye, are barely affected, the disease has killed tens of thousands of oaks in California in the past seven years. Since its discovery the alga has been found to infect 17 different tree species.
The Phytophthora genus includes about 60 species, including the pathogen that caused the Irish potato famine (P. infestans). In Australia, P. cinnamomi has devastated some forests, attacking the roots of about 20 per cent of all jarrah trees, a type of eucalyptus.
快猫短视频s guess from the virulence of P. ramorum that it probably originated in another part of the world, and might have been imported into the state on ornamental rhododendrons. 鈥淚t may be an exotic pathogen that never co-evolved with any of these plants,鈥� says David Rizzo, a plant pathologist at UC Davis who helped make the diagnosis.
Officials aren鈥檛 sure how to fight the disease. The first step is to quarantine affected redwoods and firs in a bid to slow its spread and prevent people from unwittingly passing it on.
Another option may be to douse the trees in phosphorus compounds, which kill the alga. Matteo Garbelotto, an ecologist at Berkeley, has already had some success injecting phosphonate into infected oak trees. And in Australia, jarrah disease is partially controlled by spreading phosphorus compounds on the ground.
But the approach might not work in California. Rizzo points out that it would be impractical to inject millions of trees. And spreading phosphorus in densely populated California could present health risks. Besides, the treatment might not work when the infection is in the foliage of the trees and not the roots, he says.