Date of Award

Winter 1982

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

Abstract

The degree to which seed crops in seed orchards reflect the genetic variability and superiority present among orchard parents (genetic efficiency) was examined in two loblolly pine seed orchards using seven allozyme loci as genetic markers.

The frequency of outcrossed progeny in the seed crop was estimated using unique markers, a single locus mixed mating model, and a multilocus model. These estimates were 0.982, 0.992, and 0.994, respectively. Thus, selfing did not contribute significantly to deviations from genetic efficiency in these orchards.

Pollen contamination, on the other hand, was found to have a significant impact on genetic efficiency. Unique markers in background stands were used to estimate a contamination rate of 0.28 (+OR-) 0.06. The proportion of seed in one orchard fertilized by pollen from the other orchard was estimated to be 0.10 (+OR-) 0.02.

The overall genetic efficiency of the orchards was examined by comparing the observed gene frequencies in the bulk seed crop to those expected on the basis of two models, full genetic efficiency (each clone weighted equally), and a model in which each clone was weighted by the number of ramets present. The best fit of the ovule pool gene frequencies was to the model weighted by ramets. The best fit of the pollen pool gene frequencies was to a model which incorporated pollen contamination.

Of eight markers each expected to occur at a frequency of less than five percent (based on weighting by ramets), all eight were found in both the pollen and ovule contributions to the seed crop in each of three seed years. When seed was separated into size classes, a substantial loss of clonal representation and genetic diversity occurred in each size class.

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