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most part, not too large because few environmental variables were correlated with Type B genetic
correlations. The data also were used to examine expected gains from using combinations of sites
in selection indices. Even though additional sites always increased the expected genetic gain, the
marginal increase was only minimal if 3 or 4 sites were already in the index. The trend was
consistent over all 6 breeding zones.
291. Johnson, G.R. 2002. Genetic variation in tolerance of Douglas fir to Swiss needle cast as assessed
by symptom expression. Silvae-Genetica 51(2/3): 80-86.
Keywords: genetic tree improvement
tree/stand protection
tree/stand health
growth
genetic relationships
Abstract: The incidence of Swiss needle cast (caused by Phaeocryptopus gaeumannii) on
Douglas fir (Pseudotsuga menziesii) has increased significantly in recent years on the Oregon
coast. Genetic variation in symptoms of disease infection, as measured by foliage traits, was
assessed in two series of progeny trials to determine whether these "crown health" indicators were
under genetic control and correlated with tolerance (tolerance being continued growth in the
presence of high disease pressure). Foliage traits generally had lower heritabilities than growth
traits and were usually correlated with diameter growth. Foliage traits of crown density and
colour appeared to be reasonable indicators of disease tolerance. In the absence of basal area data,
assessing crown density and colour can help screen for families that show tolerance to the
disease.
292. Johnson, G.R., R.A. Sniezko and N.L. Mandel. 1997. Age trends in Douglas-fir genetic
parameters and implications for optimum selection age. Silvae-Genetica 46(6): 349-358.
Keywords: genetic tree improvement
growth
genetic relationships
Abstract: Trends in genetic variation in Douglas fir (Pseudotsuga menziesii) were
examined over 51 progeny test sites throughout western Oregon. Narrow sense heritabilities for
height and diameter showed an increasing trend to age 25, the oldest age examined. Before age
10, height heritabilities were relatively unstable. Type B site-site genetic correlations increased
slowly with age for height and remained relatively stable for diameter. Age-age correlations were
used to develop an equation to predict age-age correlations by using the log of the age ratios
(LAR). Optimum selection age was calculated for a 60-year rotation by using two measures of
efficiency: gain per year and discounted gain. The optimum selection age for height tended to be
2 to 3 years earlier than for diameter. Gain per year was maximized at age 10 for height and age
13 for diameter.
293. Johnson, G.R., N.C. Wheeler and S.H. Strauss. 2000. Financial feasibility of marker-aided
selection in Douglas-fir. Canadian-Journal-of-Forest-Research 30(12): 1942-1952.
Keywords: genetic tree improvement
economics