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Geographic variation in seed weight, some cone scale measurements and seed germination of Douglas-fir Pseudotsuga menziesii (Mirb.) Franco Yao, Chang


The principal objectives of the study were to investigate geographic variation of, and relationship between, 1000-seed weight and cone-scale morphology and variation of germination percent of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco ) from within its natural range in Northwest America. One hundred twenty four seed sources representing eight climatic regions from British Columbia to California (lat. 38°50' to 53°37', long. 117°00' to 127°27') were collected in 1966 and 1968 by the International Union of Forestry Research Organizations, Section 22. From the seed samples, filled seed (which constituted 1000-seed weight) were selected using soft X-ray fluoroscopy. Five cone-scale measurements were taken; cone-scale width, bract width, cone-scale length, 1st prong length and 2nd prong length. The position of the bract in relation to the scale was rated. For germination testing, 56 filled seeds were selected to represent each of 12 trees in each of 114 provenances. The total of 76,608 seeds from 1,368 individual trees were sown untreated in two replications on ten relatively uniform nursery beds during May, 1969. Seed weights varied greatly. One thousand-seed weight increased clinally from low to high elevation and from north to south. Latitude appeared to affect seed weights more than elevation. Cone-scale characteristics differed significantly from tree to tree, provenance to provenance, as well as sub-region to sub- region. Cone-scale widths and lengths were only significantly different between regions. These characteristics again showed a clinal variation which increased from low to high elevations and from north to south in some regions, and revealed that latitude affected cone-scale morphology more than elevation. Thousand-seed weights were generally positively correlated with cone-scale size. Germination percent was significantly affected by latitude around 36 days after sowing, but this effect disappeared by 50 days. Elevation and longitude appeared not to affect germination percent during the observed period (0 - 92 days after sowing). The results of this study illustrate the importance of geographic origin as a source of phenotypic variability in Douglas-fir.

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