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Inbreeding and Single Crossing In Douglas-Fir

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Eight S1 selfed families of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, established in 1952 and 1954 were heavily fertilized to induce flowering in 1961. The response the following year varied considerably both within and between selfed families and only a limited number of pollinations were possible. Inbreeding reduced both size of the staminate strobili and number of sporangia in some inbreds. A cytological examination of pollen from inbreds and their open- and cross-pollinated sibs showed that, in general, the latter samples were larger. There were considerable variations in both form and length of cone between trees in a selfed family. In general, the cones were smaller than those from their open- and cross-pollinated sibs. Four mating systems were investigated: further self-pollinations to an S2 generation, full-sibbing, backcrossing, and single crossing. The yield of viable seed from the first was drastically reduced compared with other matings but the S2 seedlings were not noticeably weak. Final height measurements of the progeny, made 14 weeks after sowing, varied considerably within the respective matings. The best single cross was made with the tallest tree as seed parent. It is suggested that an inbreeding program in Douglas-fir be initiated by establishing selfed families from trees now being selected for seed orchards.

Document Type: Journal Article

Affiliations: Forester, Research Division, Forest Service, The Province of British Columbia, Victoria

Publication date: September 1, 1965

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