Early testing of Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) for Swiss needle cast tolerance Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9z903195f

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  • The relationship between the level of Phaeocryptopus gaeumannii (Rohde) Petrak colonization and severity of Swiss needle cast (SNC) symptoms, the possibility of early testing of Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) for SNC tolerance, and geographic variation in coastal Oregon with respect to SNC tolerance were investigated. Comparisons between the amount of P. gaeumannhi DNA and SNC symptom severity (i.e., degree of yellowing or loss of needles) of 6 wind-pollinated Douglasfir families (two families for each of three disease severity groups) in two progeny test plantations revealed that there were no immune Douglas-fir trees; infection and colonization of Douglas-fir needles by P. gaeumannii occurred at similar rates in the different disease severity groups. The presence of significant differences in symptom severity among the groups, therefore indicated that tolerance, rather than resistance, is responsible for the observed variation in disease symptoms. The degree to which a tree retains its last four growing season's needles appears to be a useful measure for assessing tolerance to SNC. Trees from 55 wind-pollinated Douglas-fir families were assessed for SNC symptoms in two 2-year-old (juvenile) and two 10- and 12-year-old (mature) progeny tests to investigate the genetics of SNC tolerance in Douglas-fir and the possibility of early testing. Natural inoculation was found to be suitable for early testing purposes. Traits related to SNC tolerance (i.e., needle retention, needle color, foliage color and foliage density) were under low to moderate genetic control (0.11[less than or equal to][h[subscript i superscript 2] [less than or equal to] 0.37) at both ages. Moderate genetic correlations between juvenile and mature trees for needle color (r²[subscript B] = 0.53) and needle retention (r²[subscript B] = 0.75) make these traits suitable for early selection. Early selection for needle retention in seedlings is expected to be as efficient as selection in older trees for improving needle retention in older trees, while early selection for needle color is estimated to be 52% as efficient as later selection for needle color. Two-year-old progeny of 152 wind-pollinated Douglas-fir families originating from the Siuslaw National Forest were assessed for severity of SNC symptoms in two seedling trials to investigate genetics of SNC tolerance and relationships between SNC tolerance of families with climatic and geographic variables of mother tree locations. The locations ranged between 25 and 667 m (mean = 331 m) in elevation and between 1 and 48.9 km (mean = 15.2 km) in distance to the Pacific Ocean. The southernmost and the northernmost mother tree locations were north of Florence and south of Pleasant Valley, respectively. Tolerance to SNC was found to be weakly heritable. Despite a wide range among families in severity of SNC symptoms, no significant relationships were observed between needle retention and geographic and climatic variables at mother tree locations. Foliage color in SNC infected trees, however, was significantly associated, although weakly (R² = 0.14), with geography; with greenest foliage in families originating from lower elevations, southerly aspects and midway in the west-east transect across the Coast Range Mountains (i.e., greenest at about 20 km from the coast). The lack of strong patterns of SNC tolerance may be because geographic variation in SNC infection is limited within this region or because there has not yet been sufficient selection pressure on Douglas-fir for patterns to eveolve.
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