Virginia Bioinformatics Institute researcher advances fight against sudden oak death disease

06/10/04

Blacksburg, Va., June 10, 2004 Virginia Bioinformatics Researcher Brett Tyler and his colleagues are one step closer to finding a cure for a disease affecting California oak trees that is now showing up in nurseries in a dozen states, including Virginia, and threatening woody ornamentals and East Coast forests.

Tyler and his colleagues have successfully mapped the genome of the devastating pathogens Phytophtora sojae and Phytophtora ramorum. P. ramorum, also known as sudden oak death, is a serious fungal pathogen that has attacked and killed tens of thousands of California and Oregon oak trees. P. sojae, the sister pathogen to P. ramorum, causes serious damage to soybean crops and cost growers $1 billion worldwide last year.

The sequences of P. sojae will act as a "Rosetta Stone" to help researchers better understand P. ramorum's genome makeup and uncover valuable information to help cure and prevent sudden oak death disease. In addition, the sequencing of the P. ramorum genome represents the fastest tracking time between the identification of a complex pathogen (in 2000) and the completion of its genome (in 2004).

Tyler, along with representatives from the Department of Energy Joint Genome Institute (JGI at www.jgi.doe.gov), United States Department of Agriculture (USDA), USDA Forest Service, the National Science Foundation (NSF) and others will present the scientific findings to the media on June 10, 2004 at the Joint Genome Institute in Walnut Creek, California.

Sudden oak death disease has the potential to affect forests in the Appalachian highlands in Virginia and other areas on the East Coast. The disease kills the oak tree, but usually the carrier shrubs survive. Sudden oak death has affected California redwood seedlings and sprouts, but not the trunks. However, it poses a large threat to Virginia oak trees and other Eastern Seaboard plant species that have proven highly susceptible to the pathogen in greenhouse tests. Tyler identified the Virginia highlands as a potential target for P. ramorum, as they have the cool, moist air needed for spore spread and survival.

"Sudden oak death thrives in cool and moist West Coast forests," said Tyler. "Since some Virginia forests and the Appalachian highlands have similar climates, they are in danger of being invaded by the pathogen."

According to Tyler, P. ramorum kills leaves on under-story shrubbery below the oaks, such as Virginia-native rhododendron, California bay laurel, azalea and camellia. Then spore-infected leaves fall to the ground while the shrub remains living and vibrant. From the ground, the leaf's P. ramorum spores are either blown by wind or splashed by rain to the oak's trunk where the pathogen infects the living bark layer. The P. ramorum infection spreads around the trunk's circumference and cuts off food supplies coming to the roots from the leaves, eventually killing the roots. Thus, the tree's death begins with the roots, causing the upper tree trunk, bark, limbs and leaves to die from lack of water.

The genome sequence of P. ramorum will help researchers develop better detection methods for sudden oak death, more accurately track the spreading of the disease, detect the routes of the spread, and determine if it can spread from nursery plants into the forest.

The USDA has identified ornamental shrubs imported from California infected with the disease in Virginia-based nurseries, as well as nurseries in 11 other states. As a result a nationwide quarantine has been placed on all imported shrubs from California.

In 2002, VBI in collaboration with the DOE Joint Genome Institute began this $3.8 million project, which was funded by USDA, NSF, and DOE, to sequence all genes in P. Sojae and P. ramorum.

Source: Eurekalert & others

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