Sexual reproduction of interior spruce was investigated. In a preliminary study,
seeds were produced from 50.5±20.0% of ovules in the most productive seed orchard
trees. Seed production in most trees was far lower. Development between the time of
pollination and early embryo formation was studied and reasons for low seed set are
described.
Low levels of pollination, as judged by dissection of ovules, was a problem in the
seed orchard so the pollination mechanism was studied. The seed orchard is in a hot, dry
location and there was a suspicion that pollination drops might not be produced under these
conditions. Pollination drops were secreted very late by ovules as seed cones began to
close at the end of the receptivity period. Micropylar arms withered and no longer
functioned in pollen capture by the time pollination drops were secreted. Pollen move into
inverted ovules by floating upwards within the pollination drop. Sacci, the 'wings' of
conifer pollen, function as floatation devices in the pollination mechanism. Pollination
drops are large and nearly fill the space that the micropyle occupies within the closed seed cone. Pollen adhering to the micropylar arms float within the pollination drop into the
micropyle but, as well, pollen adhering to the cone axis near the micropylar arms are
scavenged by the large drop. Rain may function in the pollination mechanism of interior
spruce and an evolutionary scenario for the pollination drop mechanism is proposed. Picea
orientalis has saccate pollen that sink into upright ovules. This is different from all other
spruce so saccate morphology was investigated. TEM revealed that the exine layer of the
sacci is porous when compared to interior spruce. Hydration of the pollen body forces air
out of the sacci as observed by confocal microscopy. Ovule orientation and pollen
floatation are described as correlated characters.
An anatomical study was made of ovule development from pollination through
fertilization and early embryo formation. Many of the observations confirm reports in the
literature but examination of resin embedded specimens has allowed for a more detailed
description of development. Many abnormalities which prevent fertilization were
observed. Because prezygotic failure other than lack of pollen is not generally considered
to be a constraint in conifer seed production, abnormal developments are described.
Abnormal ventral canal cells and nucelli account for most of the observed prezygotic seed
losses. Losses due to lack of pollen, and abnormal development were estimated at 15%
each. Self-pollination results in low seed set in conifers so prezygotic development in self-pollinated
ovules is described. Two types of prezygotic abnormality which prevent
fertilization and that occur only after self-pollination were described and the possibility that
some type of self-incompatibility mechanism might occur in conifers is discussed.
Failure at prezygotic stages is common in interior spruce but it is generally only
possible to observe these stages by doing careful study of the fertilization period. When
seeds without developing embryos are examined after the time of fertilization it is usually
impossible to tell if failure was pre-, or postzygotic. Seed losses in conifers are usually
described to result from genetic load. The degree of prezygotic failure observed in this
study suggests that conifers may not have as many embryonic lethal recessive alleles as
estimated.
Recommendations for increasing seed production in the seed orchard through
effective use of supplemental pollen and for further studies of a botanical nature are made. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/8207 |
| Date | 31 May 2017 |
| Creators | Runions, Clifton John |
| Contributors | Owens, John N. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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