Present/Past Research Summaries
Summaries by category of the major research findings involving Swiss Needle Cast (SNC) and its agent the foliar fungus Phaeocryptopus gaeumannii.

1. Effects and Impacts of SNC
2. SNC Treatments
3. Quantification, Assessment, and Severity Prediction
4. Tree Genetics, Resistance, and Improvement

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Quantification, Assessment, and Severity Prediction

The quantification of P. gaeumannii is important for future research on the ecology and epidemiology of plant pathogens, the evaluation of resistance, and investigations of foliage infection and colonization. Pseudothecial density measures (i.e. fruiting body abundance), are well correlated with symptoms such as chlorosis and needle retention but are extremely time consuming and tedious, and can be subject to errors in measurement (Winton et al. 2003). Measures of ergosterol content can be a good measure of fungal biomass in Douglas-fir but is not fungal species specific and can be influenced by presence of other fungal species (Manter et al. 2001; Winton et al. 2003). (Fig. 1A) This method is sensitive enough to quantify P. gaeumannii prior to presence of pseudothecia (Winton et al. 2003). It is relatively inexpensive, rapid, and large numbers of samples can be analyzed (Winton et al. 2003). The dot blot hybridization technique has potential to be more specific than ergosterol measurements, but has shown to cross-react with fungal species closely related to P. gaeumannii (Winton et al. 2003), limiting its usefulness when similar fungal species are present in high quantities. Real-time quantitative polymerase chain reaction (PCR) techniques have the advantage of speed, simplicity, specificity, and cost-effectiveness. It is also the only method to date with the ability to detect and quantify P. gaeumannii early in the disease cycle (Winton et al. 2003), (Fig. 1B) and works in both heavily infected/diseased foliage, as well as apparently healthy foliage (Winton et al. 2002). This method can also be applied to simultaneously quantify host and pathogen DNA, to derive a relative measurement of pathogen colonization of host tissue (Winton et al. 2002). (Fig. 1C)

The visual and physical assessment of SNC severity has been accomplished on a larger scale by developing maps (Fig. 1D) from annual aerial surveys in April and May completed from 1996 to 2006 by the Oregon Department of Forestry (Hansen et al. 2000). Flights were made at 450 to 600 meters above the terrain following a north south flight path extending from the coast line east until symptoms were no longer visible (Hansen et al. 2000). Polygons of infected patches were drawn onto topographic maps and classified as either heavy (brown foliage and very sparse crowns) or light (yellow-yellow brown foliage with slightly denser crowns (Hansen et al. 2000).

At a more local scale (e.g. stand and ownership scale) ratings of needle retention, chlorosis (needle discoloration), and P. gaeumannii sporulation have been made at the plot level (Hansen et al. 2000). Needle retention has been the primary assessment tool for foresters on the ground. Needle retention is estimated on a scale from 0 to 9, 0=0-9% of needles retained and 9=90-100% of needles retained (Hansen 2000). This score is calculated for each annual set of needles, and can be done for as many years of needles that remain on the tree. The total score for all years is then divided by the number of years to obtain a score for the tree. Maguire and others (2002) have simply divided the tree into thirds and averaged the number of needle age classes present from a secondary or lateral branch for each third. Variations on these methods have been used to determine severity as well (e.g. Rosso and Hansen 2003; Mainwaring et al. 2005) Other parameters such as foliage mass, ratios of crown measurements to sapwood area, sapwood moisture content, branch surface area and distribution, and tree basal area or growth measurements have been used to assess the impacts of SNC (Maguire et al. 2002; Weiskittel et al. 2006; Mainwaring et al. 2005; Maguire and Kanaskie 2002; Weiskittel and Maguire in press). (Fig. 1E)

Temporal and spatial variation in disease severity has been noted since the early 1990's, and modeling this variation has become a recent focus of research efforts. Initial efforts of developing prediction models (Ross and Hansen 2003) indicated fog occurrence, precipitation, temperature, elevation, and slope aspect were all important factors in predicting severity of the disease. (Fig. 1F) The number of ascocarps (pseudothecia) on tree foliage was also shown to be correlated with temperature, specifically winter temperatures, and leaf wetness in the spring affecting development of the P. gaeumannii, and over time could lead to differences in severity of SNC (Manter et al. 2005). It has also been found that fungal abundance and symptom expression is greater on warmer south-facing (western coast range) and north facing (eastern coast range) slopes (Manter et al. 2003), (Fig. 1G) presumably due to increased excess light energy at these higher light levels. Using this type of information, as well as information on dynamics of infection and colonization, a climate based disease prediction model is being developed in combination with GIS linked climate databases (Fig. 1H) to estimate disease levels across an affected portion of the Oregon Coast Range (Manter et al. 2005). Stone and Coop (2006 annual report) are pursuing a model using climate-topography relationships affecting coastal cloud, fog, and drizzle, in combination with fungal epidemiology to develop spatial models for predicting SNC distribution and severity. (Fig. 1I) These models will be useful for hypothesis testing in future studies (e.g. disease spread and intensity with climate change, affects on regional carbon budgets), as well as a decision support tool for forest managers dealing with SNC.

ODF Aerial Survey Maps

Maguire, D.A. and A. Kanaskie. 2002. The ratio of live crown length to sapwood area as a measure of crown sparseness. For. Sci. 48: 93-100.

Manter, D. K., Kelsey, R. G., and J. K. Stone. 2001. Quantification of Phaeocryptopus gaeumannii colonization in Douglas-fir needles by ergosterol analysis. For. Path. 31: 229-240.

Manter, D.K., Winton, L.M., Filip, G.M., and J. K. Stone. 2003. Assessment of Swiss Needle Cast Disease: Temporal and Spatial Investigations of Fungal Colonization and Symptom Severity. Phytopath-Z. 151:344-351.

Manter, D.K., Reeser, P.W., and J.K. Stone. 2005. A climate-based model for predicting geographic variation in Swiss needle cast severity in the Oregon coast range. Phytopathology 95: 1256-1265.

Weiskittel, A.R., Maguire, D.A., 2006. Response of Douglas-fir leaf area index and litterfall dynamics to Swiss needle cast in north coastal Oregon, USA. Annals of Forest Science 63, in press.

Weiskittel, A.R., Maguire, D.A., 2006. Branch surface area and its vertical distribution in coastal Douglas-fir . Trees 20, in press.

Winton, L.M., Manter, D.K., Stone, J.K., and E.M. Hansen. 2003. Comparison of biochemical, molecular and visual methods to quantify Phaeocryptopus gaeumannii. Douglas-fir foliage. Phytopathology. 93: 121-126.

Winton, L. M., Stone, J. K., Watrud, L. S., and E. M. Hansen. 2002. Simultaneous one-tube quantification of host and pathogen DNA with real-time polymerase chain reaction. Phytopathology. 92: 112-116.