Graduate Thesis Or Dissertation
 

Effects of seed characters and competitive environment on two-year performance of open-pollinated Douglas-fir families

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  • Ungerminated seed and recent germinants from 39 open-pollinated Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) families were planted in each of three competitive environments in order to determine the degree to which growth differences among families are influenced by competitive environment, seed weight, and date of emergence. The three competitive environments were a mixture of individuals from all families planted at a narrow spacing (4x4 cms), single (pure) family blocks planted at a narrow spacing (4xL cms), and individuals from all families planted at a wide, non-competitive spacing (16xl6 cms). Despite some large changes in the relative ranking of families between competitive environments for total dry weight, the family x competitive environment interaction was non-significant (p<O.O5). Furthermore, families did not differ significantly in competitive ability or density tolerance. Competitive environment, however, had a large effect on estimates of variance components, heritability, and genetic gain. Analysis of correlated response to selection indicated that testing and selection in mixture would result in the largest estimated gains in seedling dry weight, irrespective of the competitive environment anticipated for outplanting. Families differed significantly in seed weight, total percent emergence, and rate of emergence. Nevertheless, correlations between seed weight and rate of emergence, seed weight and seedling size, and rate of emergence and seedling size were not strong. The magnitude of the correlation between seed weight and seedling size of families was no less when germinants were used than when ungerminated seed was used. Thus, using germinants did not appear to be useful for controlling seed weight effects in this study. In addition the magnitude of the correlation between seed weight and seedling size was not influenced by interfamily competition. Genetic variation in seedling architecture (the form and structure of a seedling's crown, stem, and root system, as well as the proportion of total biomass partitioned to each) was assessed in order to explore the potential for realizing gains from ideotype breeding. Families differed significantly for all traits and estimates of heritability were mostly moderate (ranging from h2=O.07 to 0.49). Relative family performance for traits of seedling architecture was dependent upon the density at which families were grown for all traits except crown width relative to height, but intergenotypic competition did not affect relative family performance. Phenotypic relationships among traits of seedling architecture and seedling size were generally consistent across competitive environments, but genetic relationships did depend to some extent on competitive environment. These results using seedlings indicate that the potential exists to realize gains from ideotype breeding. However, relative family performance for seedling architecture traits may depend upon the density at which families are grown. Correlated responses to selection as determined by genetic correlations between traits may also depend upon competitive environment.
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