Inbreeding Experiments With the Douglas Fir

Abstract

Two young Douglas fir were self-pollinated in 1952 and results showed a wide variation in self-incompatibility, one tree producing a fair number of viable seed. It is suggested, that a considerable range of incompatibility following selfing exists within the species and that this is due to some factor that inhibits normal seed development in varying degrees. Cytological examination of material from the highly self-incompatible trees showed that the embryo aborted at an early stage following self-pollination. The harmful effects of inbreeding were clearly seen in the progeny of the one tree, there being highly significant differences in height growth when compared with seedlings resulting from controlled cross- and wind-pollination of the same tree. The importance of the selfing technique and the practical implications of inbreeding are emphasized. A few viable seeds were obtained from unpollinated cones, the resulting seedlings are very uniform, and cytological examination has shown that they are diploid. Further investigations on self-incompatibility and agamospermy in the Douglas fir are being pursued.

Breeding Douglas‐Fir

“…The early improvement efforts of Alan Orr-Ewing focused on making intensive plus-tree selections, developing inbred lines (for subsequent outcrossing), creating interracial hybrids, and testing provenances within coastal British Columbia (Orr-Ewing 1954;Orr-Ewing et al 1972;Heaman 1977). After Gene Namkoong was hired as a consultant in the early 1970s, the focus changed to using structured mating designs (e.g., half-diallels) to create a pedigreed breeding population, estimate quantitative genetic parameters, determine the size and importance of genotype by environmental interactions, and provide family information for roguing seed orchards (Heaman 1977 …”

Inbreeding in mid-rotation coastal Douglas-fir: implications for breeding

“…In coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), the early inbreeding studies of Orr-Ewing (1954, 1957 showed ID in the seed set of cone-bearing trees and height growth of trees that were dwarves and never produced any strobili (Orr-Ewing 1976). Our knowledge of inbreeding effects has been greatly advanced by Sorensen's work with Douglas-fir (and other conifers), showing that growth and survival had high ID, upwards of 80 %.…”

Pollination dynamics in a Douglas-fir seed orchard as revealed by pedigree reconstruction

“…This is the most plausible explanation for the observed high selfing rate and was further substantiated by the highly significant correlation coefficient between clonal reproductive success and selfing rate (r = 0.944, P < 0.01, N = 49). While polyembryony (Sorensen, 1982) and inbreeding depression (Orr-Ewing, 1954, 1965 are expected to promote outcrossing by favouring embryos pollinated by unrelated individuals, the passive pollination mechanism of Douglas-fir which is characterized by the "first-on, first-in" concept (Franklin, 1974), could be responsible for the observed high selfing. In Douglas-fir, pollen is entrapped and engulfed by the stigmatic tips and subsequently delivered to the nucellus without any differentiation between self and unrelated pollen (Allen and Owens, 1972;Owens and Simpson, 1982;Owens et al, 1981).…”

“…Selfing in most conifer species results in poor seed set (Woods and Heaman, 1989), decreased progeny size, reduced progeny vigor and increased susceptibility to pests (Orr-Ewing, 1954, 1965Sorensen, 1971). Under panmixia, a selfing rate of 2% is expected to occur in this seed orchard (49/49 2 ); however, an estimate of 15.2% was detected.…”