The Port-Orford-cedar, a large evergreen tree, is native to the Pacific Northwest where it plays a significant role ecologically and commercially. The quality of its wood makes it an ideal choice for decking, siding, and flooring, and in specialty products such as wooden arrows and musical instruments. It is also planted around the world as an ornamental tree and for windbreaks.
Ecologically, the tree is more drought resistant and shade-tolerant than some of its neighbors, and it is able to survive light to moderate ground fires. The Port-Orford-cedar, also known in the horticulture trade as the “Lawson Cypress,” plays a significant role in riparian zones by providing streamside shade for fish and wildlife and keeping streambanks from eroding during wet weather.
Unfortunately, this economic and ecological treasure is under a decades-long attack from a deadly root disease. The non-native pathogen Phytophthora lateralis was first detected on ornamental seedlings near Seattle, Wash., in 1923. Within a decade, horticultural production of the ornamental tree was abandoned.
Richard Sniezko, a geneticist at the Forest Service’s Dorena Genetics Resource Center in Cottage Grove, Oregon, began working to develop a genetically resistant strain of Port-Orford-cedar 23 years ago for the Forest Service and the Bureau of Land management. The root disease had people at both agencies concerned about its devastation to the regional ecosystem and impact on commercial markets. His years of work, in partnership with colleagues at Oregon State University, have identified several types of genetic resistance in the species. Sniezko recently transferred some resistant breeding stock to Oregon State University for testing and cultivation under a Material Transfer Agreement coordinated by the Forest Service Technology Transfer Officer Thomas Moreland.
“The Port-Orford-cedar used to be a multi-million dollar contributor to the horticultural sector but was de-emphasized when the Phytophthora lateralis pathogen entered the area,” Sniezko said. “Now there is potential to add another species back into the mix.”
The Port-Orford-cedar has a large genome that has never been sequenced, which made Sniezko’s task that much harder. Over time, his research identified resistance to the P. lateralis pathogen that is controlled by a single dominant gene He also a discovered a second type of resistance controlled by a combination of many genes.
“While a single dominant gene provides immunity to the disease in the near term, in a few years it could be vulnerable if a new version of the pathogen evolves that overcomes the trees’ resistance,” Sniezko explained. “Seedling families with quantitative resistance derived from a combination of many genes have less resistance to the pathogen in the short term, but this type of resistance may be more durable in the long run.” Both types of resistance area currently being used in seed orchards to provide seed for reforestation and restoration of forest ecosystems.
Under the agreement, Oregon State University will cultivate the disease-resistance stock provided by Sniezko’s breeding program with a goal of reintroducing the ornamental species back into the nursery and landscape industries. The university will also test the resistant trees as a possible rootstock for grafting special cultivars that do not possess the same disease resistance.
In addition to managing the tree breeding program, the Forest Service continues to protect surviving Port-Orford-cedar trees and stands in the national forests by restricting movement of people and machinery during wet periods where pathogen spores are abundant. Disease-resistant trees from this program are currently being planted in native forests. In the future, thanks to the resistance, Port-Orford-cedar may regain its stature in urban forests as well.