Abstract
Reproductive bud phenology from 1983 through 1989 limited potential outcross efficiency to a maximum of 58 to 87%, in a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) clonal orchard near Monmouth, Oregon. Potential outcross efficiency was calculated for 20 clones from dates of male and female bud opening and pollination mechanism information. Cool weather before bud opening of the earliest clones delayed and compressed the breeding period and resulted in a greater percentage of trees having synchronous periods of pollen release and receptive seed strobili. Length of breeding season among years averaged 20 days and ranged from 16 to 27 days. Differences in phenology significantly impacted the breeding system because the overall breeding period of the orchard clones exceeded the 8-day receptive period of individual clones by two or three times and often prohibited or limited potential outcrossing between the earliest and latest clones. Outcrossing was greatest in clones with intermediate phenology and least in the earliest clones. The breeding system appears to be an almost continuous series of overlapping breeding subpopulations. Each year's breeding subpopulations were different from those of other years because of large shifts in rank order of bud opening by 10 to 20% of the clones and because of great differences in the length of breeding season. Average temperature during March was linearly associated with time of floral bud opening. Geneticists may be able to use average temperature of the 4-week periods prior to opening of the earliest floral buds as a tool to identify seed crops formed during years with compressed breeding seasons. Such seed crops have potential of being more diverse than do seed crops produced during years with extended breeding seasons. Use of procedures in this report will allow tree-improvement workers to calculate the maximum outcross efficiency of each seed crop produced by their orchards.
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