Estimates of pollen contamination and selfing in a coastal Douglas-fir seed orchard

Abstract

Seed orchards are the link from tree breeding to reforestation programs and are theoretically expected to function as closed, perfect populations, ensuring gain and diversity are consistently and predictively delivered as improved seed and seedlings. Seed orchard populations often deviate from panmixia due to fertility variation, reproductive asynchrony, and gene flow, leading to reduced seed crops genetic quality. Here, as a part of multiyear monitoring study, we used DNA fingerprinting (simple sequence repeat markers) to assess a Douglas-fir (Pseudotsuga menziesii) seed orchard's seed crop genetic quality (2009 seed crop). The studied seed crop was produced under ambient temperature (i.e. no reproductive phenology manipulation) and pollination was augmented by pollen from within orchard's pollen donors. DNA fingerprinting of the parental population (66 parents) along with 207 gametophyte (1n) – embryo (2n) pairs of random bulk sample of seed allowed parentage (maternal and paternal) assignment and the direct assessment of pollen contamination (0.18 ± 0.027) and selfing (0.17 ± 0.025) rates as well as parental (pollen, ovule and individual parent) gametic contribution was compared to a previous year's crop (2005). The extended reproductive phenology coupled with variable within-orchard pollen availability has created opportunities for both self and foreign pollen to be successful at various times resulting in the seemingly paradoxical scenario of high selfing and gene flow. These results (2005 and 2009) allowed comparison of seed orchard's crop management practices and are expected to provide scientific foundations to effective seed crops genetic quality improvement.