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NIFA Collaborates on Responses to Phytophthora ramorum (P. ramorum)

NIFA is one of several Federal agencies involved in a national effort to control Phytophthora ramorum (P. ramorum). Impacting over 64 plant species, this disease could have global economic implications for forest, horticultural, and agricultural industries. Seven nations, including the U.S., have imposed P. ramorum-related emergency quarantines restricting the shipment of rhododendron and other horticultural host plants, logs, and other woody materials. The effort to control P. ramorum involves both extension and research activities, and NIFA is involved in both.

The Threat Posed by P. ramorum

Phytophthora ramorum threatens our nation’s oak woodlands, urban forests, horticultural industries, and landscapes. One of the diseases resulting from Phytophthora ramorum infection is Sudden Oak Death (SOD), which kills coast live oak, tanoak, and California black oak trees. Initially observed in a limited number of oak species, P. ramorum is now known to infect the leaves and twigs of common ornamental nursery plants, such as rhododendron and camellias, which serve as vectors for pathogen dispersal.  The pathogen is reported to infect over 64 plant species, representing 36 genera of plants, including popular herbaceous plants and woody trees.
Phytophthora ramorum was first identified in 1993 in Germany and The Netherlands on ornamental rhododendrons. Since 1995, Tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia) and black oak (Quercus kelloggii) trees have been reported dying in large numbers in several coastal counties in California.   P. ramorum was isolated in June 2000 from dying trees in California. The initial outbreak occurred in the urban-wildland interface of central, coastal California -- home to over 7 million people—where falling trees and increased fire risks threaten homes, buildings, power lines, roads, watercourses, and recreation areas.
In spring 2004, potentially infected nursery grown ornamental plants were shipped throughout much of the United States. Since P. ramorum is a quarantine pathogen, inspections were conducted and infected plants recovered and destroyed at over 172 sites in 22 states. The total includes three residential finds.

Diagnosing P. ramorum

Diagnosing Phytophthora ramorum plant diseases based solely on visual symptoms is not possible. The visual symptoms of P. ramorum vary among host species, and other factors may produce similar symptoms. The pathogen causes progressive tip dieback and extensive bleeding cankers on the stems of its major hosts, usually killing them.  Additionally, foliar infections that can progress to stem infections are possible on less susceptible hosts. Symptoms on the foliage can look like leaf spots and blotches, leaf scorch, or sunburn. Even other species of Phytophthora may produce visual plant symptoms similar to those produced by Phytophthora ramorum.  A systematic approach to gathering information about suspect plants helps direct the diagnosis and reduce the risk of overwhelming plant clinics with false plant samples.

Combating P. ramorum: Extension efforts

Several national and state agencies have teamed to fight the disease through extension-related efforts:

  • NIFA;
  • The NIFA-funded National Plant Diagnostic Network (NPDN) and Regional Integrated Pest Management Center;
  • USDA Forest Service and Animal and Plant Health Inspection Service;
  • state departments of agriculture, and:
  • various state Cooperative Extension Services.

The NIFA effort involves providing educational materials for training Cooperative Extension Service faculty and Extension Master Gardeners (EMGs) to diagnose the diseases, provide plant diagnostic services, and develop plans to handle infected plants in landscapes (see Phythopthora Ramorum Educate to Detect (PRED) website).  An estimated 150,000 EMGs are located within counties across much of the U.S. Their main function is to work with homeowners on landscape, lawn, and garden issues. They have in the past been involved in other similar rapid response pest control efforts, including campaigns directed at Gypsy Moths, Purple Loosestrife, Garlic Mustard, and several other invasive species.

This effort is coordinated through the Phythopthora Ramorum Educate to Detect (PRED) program, which is managed by the National Plant Diagnostic Network and Regional Integrated Pest Management Centers. On October 26, the PRED program brought together 731 participants at 115 sites nationwide for a P. ramorum-related training session. At each site participants included EMGs, state agriculture department representatives, as well as land-grant university and cooperative extension personnel to tailor their states specific response and actions on Phytophthora ramorum in home landscaping.

Combating P. ramorum: NIFA Research efforts

In 2003-2004 NIFA supported 23 P. ramorum projects at land-grant universities through $600,00 in Hatch, McIntire-Stennis formula grants and other sources. NIFA also provided $317, 000 in Congressionally-directed funding for P. ramorum-related research in California.
Among the Hatch funded projects is the Rapid Response Research Program, W501: Management of Phytophthora ramorum in U.S. Nurseries. At a W501-related meeting in October, 2004, in Corvallis, Oregon;, 30 researchers from across the nation met to exchange information and coordinate research and extension activities concerning P. ramorum management.

On June 10, 2004, researchers with the Interagency Microbial Genome Sequencing Program (IMGSP) unveiled the genome of Phytophthora ramorum, based on work conducted at the Department Of Energy Joint Genome Institute and the Virginia Bioinformatics Institute. The IMGSP is funded by NIFA’ National Research Initiative, the National Science Foundation and the Department of Energy. The P. ramorum genome sequencing, the first sequencing of a Phytophthora species was accomplished in approximately 2 years. This fast tracking from identification of a new plant pathogen to the completion of its genome will enable rapid and more accurate diagnosis.

Related NIFA contacts

Kitty Cardwell, USDA NIFA PAS National Program Leader for Plant Pathology,

Ann Lichens-Park, USDA NIFA NRI National Program Leader for Microbial Genomics



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