Detection, identification, and management of root diseases caused by Onnia in recreation areas

Tomentosus root disease caused by Onnia spp. (e.g., O. tomentosa) primarily affects spruce (Picea spp.) and pine (Pinus spp.) in North America but has also been found in association with Douglas-fir (Pseudotsuga menziesii), true firs (Abies spp.), and western larch (Larix occidentalis) in the northern Rocky Mountains. The damage caused by this disease can be severe, leading to growth reduction, mortality, and windthrow. Diagnosis of this disease is challenging, as fruiting bodies of these fungi are ephemeral, and the characteristic decay is not visible until the roots are exposed due to windthrow or stumps are created after felling. Detecting this pathogen in standing trees is particularly difficult because it can be present for long periods of time without causing symptoms, and it often occurs deep in the root system.

Early detection of the disease is crucial, particularly in recreation areas where infected trees become hazardous and pose a threat to public safety. Infected trees are predisposed to windthrow even in the absence of outward symptoms. This pathogen has caused serious problems in Montana, where large Engelmann spruce trees have fallen in and around recreation areas. Several campgrounds have already had to be clear-cut to remove susceptible or infected Engelmann spruce trees.

The presence of white pocket rot has been used as a diagnostic feature of tomentosus root disease.  However, there may be two or more species of Onnia causing disease on conifer hosts in western North America. Characterizing the relationships between pathogen and host tree species will be important in outlining management recommendations and stand rehabilitation options for vegetation management planning in high use recreation areas. 

Approach

This project will provide a rapid field-based method for detecting and identifying Onnia spp. in wood samples from standing trees or stumps. Surveys are currently being conducted in and around recreation areas (e.g., campgrounds) with previously reported impacts from Onnia. During surveys, fungal fruiting bodies are collected, if present, and wood samples are extracted from standing trees with the aid of an increment borer. Fungi isolated from the wood samples are then subjected to genetic characterization using polymerase chain reaction (PCR) and DNA sequencing. To date, samples have been collected from various conifer hosts in Montana, Wyoming, Utah, Colorado, New Mexico, Arizona, and Oregon.

Genetic markers that allow for differentiation among species will be used for the development of a loop-mediated isothermal amplification (LAMP) assay. This rapid field-based molecular detection method allows for highly sensitive and specific detection of pathogen DNA directly from environmental samples such as decayed wood. The presence of pathogen DNA will result in a color-change reaction that can easily and unambiguously be interpreted by the user. Minimal training is required to learn this technique and it does not require access to a laboratory. These tools will allow for very sensitive and precise early detection of Onnia within individual trees enabling land managers to implement proactive management strategies to mitigate disease impacts and improve public safety in recreation areas.

The sampling protocols will be developed in conjunction with FHP specialists in each of the participating regions such that they will learn and help develop methods for use of the LAMP tool. At the end of this project all tools and information will be made available to land managers and recreation staff to use in conducting routine surveys or monitoring for tomentosus root disease. LAMP toolkits will be distributed to collaborators for running tests in the field. Videos and field-based trainings/workshops will also provide instruction on the use of the toolkits and associated protocols so that field staff can deploy them independently.

This research will identify new avenues for research to describe the ecology and epidemiology of Onnia spp. and may also inform the future development of new management strategies to address tomentosus root disease.