Sudden Oak Death Pathogen Apparently Mutating - New Limits On Plant Shipping Urged - ENN

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The pathogen responsible for Sudden Oak Death first got its grip in California's forests outside a nursery in Santa Cruz and at Mt. Tamalpais in Marin County before spreading out to eventually kill millions of oaks and tanoaks along the Pacific Coast, according to a new study led by researchers at the University of California, Berkeley. It provides, for the first time, evidence of how the epidemic unfolded in this state.

"In this paper, we actually reconstruct the Sudden Oak Death epidemic," said Matteo Garbelotto, UC Berkeley associate extension specialist and adjunct professor, and principal investigator of the study. "We point to where the disease was introduced in the wild and where it spread from those introduction points."

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Garbelotto presented these findings April 16 at the annual meeting of the California Oak Mortality Task Force, a coalition of research institutions, public agencies, non-profit organizations and private industry formed to coordinate management, research, outreach and policy efforts surrounding Sudden Oak Death disease in California. Garbelotto is a member of the task force. Up to 100 percent of adult tanoaks have been killed by the Sudden Oak Death pathogen in many sites around the Big Sur region (Monterey County). Despite the extreme severity of the disease, the pathogen was introduced in the Big Sur region well after its introduction in Santa Cruz and Marin counties. Unfortunately, climatic conditions favorable to the pathogen have led to very rapid spread of SOD in this area.

The researchers analyzed genetic markers of nearly 300 samples of the fungus-like pathogen, Phytophthora ramorum, taken from 14 forest stands in Humboldt, Sonoma, Marin, Santa Cruz and Monterey counties. The sites were chosen to represent the geographic range of Sudden Oak Death infestation and included newly infected areas as well as regions that had relatively old infestations. Samples from the wild were compared with an additional 15 P. ramorum isolates collected from nurseries in 12 states. From the samples, the researchers identified 35 unique strains of the pathogen. A computer analysis further revealed how those strains were related to each other. The study found that all strains were originally derived from three basal strains that were most prevalent in the samples and common in all sites.

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http://www.enn.com/ecosystems/article/35036