POLLEN CONTAMINATION EFFECTS ON PROGENY FROM AN OFF-SITE DOUGLAS-FIR SEED ORCHARD

The effects of background pollen contamination were evaluated for firs t-year height growth pattern of seedlings originating from a Douglas-f ir (Pseudotsuga menziesii (Mirb.) France) coastal-interior transition zone seed orchard located on southern Vancouver island, British Columb ia. Pollen collected from five stands surrounding the orchard (backgro und pollen) and pollen from five half-sib families of the seed orchard were applied to six individual trees in the orchard. The resulting 60 seed lots were raised outdoors in a coastal-climate nursery with five seed lots collected from wild stands of the transition zone. Heights were measured in 10-day intervals during the growing season. Final hei ghts, maximum height growth rate, and growth cessation were subjected to analysis of variance. Growth rate and cessation were derived from d ata fitted to the logistic growth curve using nonlinear regression ana lysis. Seedlings sired by the background pollen had significantly grea ter final heights and growth rates. There were no differences in orcha rd seedlings in growth cessation probably because all seedlings were e xposed to a blackout treatment to force bud set in mid-August. The ave rage final height of wild-stand seedlings from the transition zone was 15% and 21% lower than that of pure orchard seedlings and seedlings s ired by the background pollen lots, respectively. Standard deviations for measured traits were similar between orchard seedlings sired by ba ckground pollen and orchard pollen. If pollen contamination is not pre vented, the faster growing seedlings sired by the background pollen ma y be preferentially selected during culling in the nursery and outplan ted on sites to which they are maladapted.