Port-Orford-cedar mortality along Little Bald Hills Trail in Redwood National Park.
Port-Orford-cedar mortality along Little Bald Hills Trail in Redwood National Park.
An operational program to develop Port-Orford-cedar (Chamaecyparis lawsoniana) resistant to the exotic root pathogen Phytophthora lateralis was initiated by the USDA Forest Service in 1997. Earlier efforts starting in 1989 helped develope protocols to be used. Working in cooperation with Oregon State University, over 10,000 parent trees from natural stands in Oregon and California have been selected and have undergone initial resistance testing. Public lands (federal, state, and county) as well as an array of industrial and non-industrial lands have been surveyed for the presence of resistant Port-Orford-cedar (POC). Fortunately, although relatively rare, parent trees with high levels of genetic resistance exist in natural populations. This program will bring together these parents to produce resistant seed for reforestation and restoration. The first large quantities of resistant seed were harvested in fall 2002, and seed is being sown in early 2003 for restoration plantings.
Objectives of the program include identifying the amount and type of genetic resistance present in natural populations of Port-Orford-cedar, and developing durable resistance to this exotic pathogen while retaining the genetic diversity within the species. Studies to examine possible mechanisms of resistance to P. lateralis began in 2000. Control crosses at Dorena Genetic Resource Center eamong some of the most resistant selections are now under test and advance-generation breeding has begun. Rooted cuttings and seedlings of resistant and non-resistant material are being evaluated in greenhouses and in the field.
Past or current studies examining the genetic diversity within Port-Orford-cedar have involved isozyme studies, as well as both short-term and long-term common garden studies. Zones for seed movement are based on these studies.
Genetic resistance is only one management tool being used to stem the threat of this introduced pathogen. Resistant material can be used to restore this species on forested areas where it has been severely impacted by the disease, but other management tools such as road closures, vehicle washing, and education are being used to prevent or minimize the spread of the disease organism.
Port-Orford-cedar has been a valuable ornamental species worldwide. Its importance in Oregon and Washington has drastically diminished with the introduction of this very destructive pathogen. Development of resistance should also lead to benefits to the horticultural industry.