Guest post by Monica Lewandowski (@MMLewandowski52)
Sudden oak death is a disease that has killed millions of oaks (Quercus spp.) and tanoaks (Notholithocarpus densiflorus) in the western United States. First detected in California in the mid 1990s, it continues to steadily spread through northern California and Oregon forests, with the potential to wreak more havoc in forests and landscapes across the world.
The underlying cause of sudden oak death is a fungal-like organism, Phytophthora ramorum. The spores of P. ramorum are spread by wind, rain and human movement of infected plants. And more bad news – P. ramorum can infect much more than oaks. A strain of P. ramorum that infects larch trees is making headlines in the United Kingdom, where it’s better known as larch tree disease. Several species of trees and shrubs, herbaceous plants and even maidenhair fern are on P. ramorum‘s “host” list (view regulated plant list in the United States). This is a cause for concern as losing one or more key plant species in a forest can lead to dramatic changes for both the flora and fauna of an ecosystem.
Unfortunately, it is very difficult to halt or even manage the spread of a plant disease, especially in a forest setting. In the face of an exotic pathogen or pest, native plants often have no natural defenses. Cutting down and removing infected trees is difficult, costly, and often futile. And even if chemical treatments are available, it’s usually an impractical or environmentally unfavorable option.
The most promising long-term approach makes use of the disease resistance that is already present in tree populations. Scientists at The Ohio State University, University of California-Berkeley and the U.S. Forest Service have identified resistance to P. ramorum in native populations of coast live oak (Quercus agrifolia) in California. Anna Conrad, a Ph.D. graduate in plant pathology at Ohio State, and her faculty advisor Pierluigi Bonello carried out further research to characterize chemical compounds in coast live oak that had been associated with resistance.
Conrad used tools of analytical chemistry to develop a “chemical fingerprint” that can distinguish between resistant and susceptible trees. Importantly, the methods can be carried out without damaging or destroying the tree. Using the chemical data, advanced statistical models were employed to predict whether a tree will be resistant to sudden oak death, and thus likely to be one of the “lucky ones” to survive. “This is the first time anyone has been able to come up with a method to predict resistance to a forest tree disease in natural populations in the field,” said Bonello.
This research has important implications for forest conservation and management. Bonello points out that knowing how many resistant trees there are in a given population can guide management decisions, including whether a more “hands-off” approach is warranted, that is, letting susceptible trees die and resistant trees become established over time. These methods may also have applications for other forest tree diseases – testing is currently underway – and technological advances should make the equipment for these methods more affordable and user-friendly in the field.
Although not a cure, being able to predict whether a tree is likely to “live or die” will help us manage the spread of sudden oak death and possibly other diseases – a scenario that is likely to become more common in the future.
Conrad AO, Rodriguez-Saona LE, McPherson BA, Wood DL and Bonello P. 2014. Identification of Quercus agrifolia (coast live oak) resistant to the invasive pathogen Phytophthora ramorum in native stands using Fourier-transform infrared (FT-IR) spectroscopy. Front. Plant Sci., 14 October 2014 | http://dx.doi.org/10.3389/fpls.2014.00521
Conrad AO and Bonello P. 2016. Application of Infrared and Raman Spectroscopy for the Identification of Disease Resistant Trees. Front. Plant Sci., 07 January 2016 | http://dx.doi.org/10.3389/fpls.2015.01152
About the author: Monica Lewandowski is an assistant professor, clinical professional practice in the Department of Plant Pathology at Ohio State, where she is actively involved outreach and science communication.