Allozyme inheritance, heterozygosity and outcrossing rate among Pinus monticola near Ladysmith, British Columbia

Abstract

Analysis of megagametophytic and embryonic allozyme variants in nine enzymatic systems encoded by 14 loci was conducted on 30 western white pine (Pinus monticola Doug!.) trees from a natural stand on Vancouver Island, B.C. The segregation of allozymes in megagametophytes of heterozygous trees indicated distinct, simple, Mendelian inheritance. The stand heterozygosity parameters (proportion of polymorphic loci (0.64), average number of alleles per locus (1.79), and average expected heterozygosity (0.18)) were identical to those reported from a broadly-based survey of the species (Steinhoff et al., 1983). Comparison of progeny (viable embryo) and parental genotypic distributions indicated a major genetic shift between the two life-cycles phases. Among the progeny, heterozygotes occurred less frequently than expected under panmixia, while the reverse was observed for the parental population. Single-locus estimates of outcrossing rate varied between 0.751 and 1.043 and were significantly heterogeneous. Comparison between the single-locus estimates and the multilocus estimate (0.977) of outcrossing rates indicated that most of the inbreeding detected was due to consanguineous matings, rather than selfing. This form of inbreeding was consistent with the clustering of genotypes in the stand. Single-tree estimates of outcrossing rate varied considerably among trees and ranged between 0.682 and 1.207, indicating that some trees might possess high self compatibility and tolerate high selfing, or that violation of mixed-mating assumptions occurred. The implications of the apparent inbreeding on the derivation of genetic estimates from open-pollinated seeds and on seed crops for production plantations are discussed.

Mating patterns and pollen dispersal in a natural knobcone pine (Pinus attenuate Lemmon.) stand

“…The high rate of outcrossing observed in knobcone pine is consistent with estimates for other pine species (Fumier & Adams, 1986;Perry & Dancik, 1986;El-Kassaby et a!., 1987;Muona & Harju, 1989;Burczyk, 1991), and for conifers in general (Adams & Birkes, 1991;Mitton, 1992). Only in a few conifers have t estimates less than 80-90 per cent been reported (Perry & Knowles, 1990;Xie et al, 1991;El-Kassaby et a!., 1994).…”

Outcrossing rates as related to plant density in Phlox drummondii

“…This is contrary to the norm for crossfertilizing species (Brown, 1979;Yazdani et a!., 1985;El-Kassaby et al, 1987;Shea, 1987;Burdon et aL, 1988). The only other example of an outcrosser having a higher adult fixation index that we are aware of involves Eucalyptus delegatus (Moran and Brown, 1980).…”

The mating system in a Scots pine clonal seed orchard in Poland

“…It is interesting that the averages of individual tree outcrossing rates are very often greater than the multilocus estimates for a population (Neale and Adams, 1985;Ritland and El-Kassaby, 1985;El-Kassaby et al, 1987; and the present study), which is usually due to the influence of some trees with an outcrossing rate estimate exceeding unity. For multilocus estimates values of outcrossing greater than one are possible if the proportion of detectable outcrosses in the progeny sample is greater than that expected on the basis of detection probability for an individual tree (Neale and Adams, 1985 (Brown et al, 1984), especially when t is near 1 and sample sizes are small (Adams and Birkes, 1991).…”