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

Gaining tree genetic information in relation to Swiss Needle Cast (SNC) severity is an important step in designing programs to develop Douglas-fir tolerant to SNC. Foliage traits, crown density and color in particular, are reasonable indicators of SNC tolerance, but are under genetic control to a lesser degree than growth rates. However, since growth-increment data are not always readily available for use in breeding programs, foliage traits can be a valuable tool. Maguire et al. (2002) found needle retention a good predictor for growth loss at the stand level, and crown density may be the single best predictor (Johnson 2002).

Tolerance to SNC and not resistance seems to be the important factor in genetic variation in SNC symptoms due to infection by P. gaeumannii (Temel et al. 2004; Temel et al. 2005). (Fig. 1) Genetic selection for SNC tolerance at the seedling stage can be effective for increasing tolerance in older trees (Temel 2005). Early testing of seedlings can be effective by a) elimination of poorly performing families at seedling stage before further testing, and b) a means of quickly screening large numbers of already selected families so the most SNC tolerant individuals can be used for seed orchards (Temel 2005). Selection of D-fir genotypes with shorter needle longevity could increase forest productivity by removing infected needles sooner, and thus limiting the net drain on carbon assimilation and growth (Manter et al. 2003).

Johnson, G.R. 2002. Genetic variation in tolerance of Douglas-fir to Swiss needle cast as assessed by symptom expression. Silv. Gen. 51: 80-86.

Kastner, W., Dutton, S., and D. Roche. 2001. Effects of Swiss needle cast on three Douglas-fir seed sources on a low-elevation site in the northern Oregon Coast Range: Results after five growing seasons. West. Jour. of Ap. For. 16(1):31-34.

Temel, F., Johnson, G.R., and J.K. Stone. 2004. The relationship between Swiss needle cast symptom severity and level of Phaeocryptopus gaeumannii colonization in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii). Forest Pathology 34: 383-394.

Temel, F., Johnson, G.R., and W.T. Adams. 2005. Early genetic testing of coastal Douglas-fir for Swiss needle cast tolerance. Can. J. For. Res., 35: 521-529.

Figure 1: Relationship between natural logarithm of Phaeocrpytopus gaeumannii DNA content in 1999 needles [log(DNA99)] and average needle retention of the last four growing seasons (NR) for mild, moderate and severe disease svereity groups. Regression equations and their R-squares are given for each disease severity group. (Temel, Johnson, and Stone, 2004)

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