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

The effects of Swiss Needle Cast (SNC) are most severe in Douglas-fir (Pseudotsuga menziesii) plantations on coastal sites of northwestern Oregon where Sitka spruce and western hemlock or red alder predominated previously (Hansen et al. 2000). General symptoms of the disease include chlorosis, decreased needle retention, and reduction in height and diameter growth. Height growth can be reduced by ~ 25%, and basal area growth losses of 35% in heavily infected stands has resulted in 23% (average over target population) to 52% (sites with highest infection levels) volume loss (Maguire et al. 2002). (Fig. 1A) (Fig. 1B) Loss of foliage was found to be the predominant mechanism reducing growth. Mainwaring et al. (2005) found similar declines in basal area growth and volume.

(Fig. 1C) Infection occurs in newly emerging current-season needles with fruiting bodies (pseudothecia) emerging late in the first year west of the Oregon Coast Range (Hansen et al 2000). Needle abscission generally occurs once 50% of stomata are occluded (Hansen et al. 2000). (Fig. 1D) (Fig. 1E) Other studies indicate this coincides with ~25% pseudothecial density and the occurrence of a negative carbon balance in the needle (Manter et al. 2003). Models indicate that photosynthesis from unaffected 1st year needles continues unhindered for up to 6 months. Therefore, net carbon gains at the whole canopy level remain positive (Manter et al. 2003). Excess absorbed light in infected needles combined with decreased photosynthetic capacity has been shown to cause photoxidative damage which may also contribute to premature needle loss in sun exposed foliage (Manter 2002). (Fig. 1F) Pseudothecia, emerging from needle stomata, impede gas exchange (Manter et al. 2000), reduce stomatal conductance in remaining functional foliage, (Manter and Kavanagh 2003) and decrease CO2 assimilation up to 3 fold (Manter et al. 2000; Manter 2002). (Fig. 1G) The fungus also appears to gain nutrients from intercellular spaces of needles, possibly by altering membrane permeability (Hansen et al. 2000). Soil nutrient additions have revealed that P. gaeumannii responds to nutrient status in host trees and that increased N-availability in D-fir needles is related to severity of SNC (El-Hajj et al. 2004). (Fig. 1H)

The distribution of foliage mass in infected trees can be altered as well, with the youngest age class foliage shifting towards the upper crown, while older age foliage shifted toward the base of the crown (Weiskittel et al. 2006). (Fig. 1I) Reduced foliage retention in upper crown corresponds to earlier findings regarding excess absorbed light and needle abscission (Manter 2002). Both leaf area and wood surface area are decreased with increased SNC infection intensity/severity (Weiskittel and Maguire in press). Reductions in leaf area, sapwood area, and permeability (Manter and Kavanagh 2003) relate to decreases in hydraulic conductance (Manter and Kavanagh 2003). (Fig. 1J) Wood density and latewood proportion were much higher in stands heavily infected with SNC (Johnson et al. 2005). Annual growth (ring width) decreases, a result of lower needle retention, were most correlated with these changes in wood properties. (Fig. 1K) Finally, ethanol concentrations (possible beetle attractant), wound-induced resin flow, and beetle attraction were all reduced as SNC severity increased. (Fig. 1L) However, the number of attacks did not decline, and success of attacks (penetration depth and gallery length) increased most likely due to weakened defense mechanisms (oleoresin defense) of the tree (Kelsey and Manter 2004). (Fig. 1M)

Hansen, E.M., Stone, J.K., Capitano, B.R., Rosso, P., Sutton W., Winton L., Kanaskie A., and M.G. McWilliams. 2000. Incidence and impact of Swiss needle cast in forest plantations of Douglas-fir in coastal Oregon. Plant Disease. 84: 773-779.

Johnson, G.R., Grotta, A.T., Gartner, B.L., and G. Downes. 2005. Impact of the foliar pathogen Swiss needle cast on wood quality of Douglas-fir. Can. J. For. Res. 35: 331-339.

Kelsey, R.G., and D.K. Manter. 2004. Effect of Swiss needle cast on Douglas-fir stem ethanol and monoterpene concentrations, oleoresin flow, and host selection by the Douglas-fir beetle. For. Ecol. Man. 190: 241-253.

Maguire D.A., Kanaskie A., Voelker W., Johnson R., and G. Johnson. 2002. Growth of young Douglas-fir plantations across a gradient in Swiss needle cast severity. West. Jour. of Ap. For. 17: 86-95.

Manter, D. K. 2002. Energy dissipation and photoinhibition in Douglas-fir needles with a fungal-mediated reduction in photosynthetic rates. J. Phytopathol. 150: 674-679.

Manter, D.K., Bond, B.J., Kavanagh, K.L., Rosso, P.H., and G.M. Filip. 2000. Pseudothecia of Swiss needle cast fungus, Phaeocryptopus gaeumannii, physically block stomata of Douglas-fir, reducing CO2 assimilation. New Phytologist 148: 481-491.

Manter, D.K., Bond, B.J., Kavanagh, K.L., Stone, J.K., and G.M. Filip. 2003. Modelling the impacts of the foliar pathogen, Phaeocryptopus gaeumannii, on Douglas-fir physiology: net canopy carbon assimilation, needle abscission and growth. Ecological Modeling. 164: 211-226.

Manter, D.K., and Kavanagh, K.L. 2003. Stomatal regulation in Douglas-fir following a fungal-mediated chronic reduction in leaf area. Trees : structure and function. 17:485-491.

Rosso, P.H., and Hansen, E.M. 2003. Predicting Swiss Needle Cast distribution and severity in young Douglas-fir plantations in coastal OReogn. Phytopathology. 93 (7):790-798.

Figure 1A: Trends in estimated cubic volume growth loss(%) for the range in average foliage retention (yr) observed on 70 sample plots in 1996. Growth was not significantly related to foliage retention in any year prior to 1990. (Maguire et al., 2002)

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Figure 1B: Periodic annual volume increment implies by model [2], assuming approximately mean values for site index (38.0 m, 50 years), crown length (16.68 m), and relative density (5.04). Cl:SA, crown length / sapwood area ratio. (Mainwaring et al., 2005)

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Figure 1C: Seasonal patterns of Phaeocryptopus gaeumanii infection in inoculated 2-yr-old Douglas-fir seedlings (open circles, infected; closed circles, control). For each sample date treatment differences were tested using a paired t-test; *, P<0.05. (Manter et al., 2000)

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Figure 1D: Needle retention for infected and non-infected saplings at three Douglas-fir plantations (May 1990). Each observation is the mean (n=6) and error bars are one standard error. Current-, one- and two-year refer to the needle age. (Manter and Kavenagh, 2003)

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Figure 1E: Total leaf area (all age classes) versus cross-sectional stem area (1997 node) for 3-year-old branches from field trees with varying levels of Phaeocryptopus gaeumanii infection and defoliation (September 2000). Eaceh observation is the mean (n=3) and error bars are one standard error. (Manter and Kavenagh, 2003)

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Figure 1F: Response of net C0₂ assimilation (A_net) to increasing irradiance. Each obsevationis the arithmatic mean and individual standard error for six seedlings. (Manter, 2002)

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Figure 1G: Total long-term estimate of net CO₂ assimilation (A_net) per unit leaf area in relationship to [panel A] P. gaeumannii pseudothecia density (%) or [panel B] needle retention (%, April 2000). A_net is the modelled value for each needle age class present within a plot; pseudothecia density is the average percentage of stomata with visible pseudothecia from six trees. (Manter et al., 2003)

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Figure 1H: Current, 1-, 2-, and 3-yr-old Douglas-fiir (pseudotsuga menziesii) needles sampled in Oct 2002 following different levels of soil N applications control (CK, diamon), low urea (LU, square), and high area (HU, triangle). (a) Percent N (%), (b) nitrogen stable isotope ratio (8¹⁵N), (c) percent carbon (%C), and (d) carbon stable ratio (8¹³C). * Indicates significantly different values within an age class. Bars represent SE, n=5. (El-Hajj el al., 2004)

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Figure 1I: Estimated relative vertical distribution of foliage mass density ((kg·m^-1 froma ll age-classes and for trees with different Swiss needle cast severity (a) and plantation age(b). (Weiskittel et al., 2006)

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Figure 1J: Branch leaf specific conductance (K_{L_B}) versus the percent of latewood present in sapwood cores taken at breast height from field trees with varying levels of Phaeocryptopus gaeumannii infection and defoliation. Each observation is based on one tree, conductance values for a given branch node (e.g., 1998) are plotted against the percent latewood for the corresponding annual increment (e.g., 1998). (Manter and Kavenagh)

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Figure 1k: Relationships between needle retention and (a) MOE, (b) MOR, (c) ring density and latewood proportion, and (d) rings per centimeter. Each point is the mean for a stand. (Johnson et al., 2005)

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Figure 1L: Relationship between phloem ethanol content and beetles captured in the barrier traps using individual tree totals (panel A) and plot averages (panel B) for the B-M and B-L plots at the Beaver site. (Kelsey and Manter, 2004)

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Figure 1M: Relationsip between the percent of attackes penetrating to the sapwood and sapwood a-pinene content for the B-M and B-L trees at the Beaver site. (Kelsey and Manter, 2004)

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