Reproduction de : Thèse de doctorat : Sciences Naturelles : Faculté des sciences de Paris : 1879. / Titre provenant de la page de titre du document numérisé.

Blue-flowered Conospermum are endemic to Western Australia, and show great potential as cut flowers. Propagation from cuttings or seed proved difficult, and root initiation in vitro is problematic. This thesis examines the floral biology of the species and the possibility of using somatic embryogenesis to overcome propagation problems. A survey of explant tissue types for C. eatoniae and C. caeruleum was carried out to identify tissue that could be induced into embryogenic pathways. Vegetative, semi-floral and floral buds were initiated into culture from February to June, but were found unsuitable for embryogenesis, producing shoots, callus or dying in culture. Leaves from in vitro leaf cultures formed callus in the presence of 2,4-D and BAP, but were unable to differentiate into embryos in the presence of a variety of growth regulator combinations and concentrations. Immature zygotes died in culture. Direct embryogenesis and/or embryogenic callus was observed on mature zygotes of the species C. caeruleum, C. spectabile, C. dorrienii and C. brownii, and somatic embryos were maintained in culture for up to 18 months for C. caeruleum. Maturation and germination of somatic embryos proved difficult; treatments of cold, ABA, desiccation or mannitol did not induce maturation. It appears that developmental pathways in Conospermum are well defined and are difficult to alter in vitro. It was concluded that somatic embryogenesis has limited commercial potential in these species. Conospermum species have an active pollination mechanism where the style is held in a state of tension when the flower opens. When pressure is applied at the base of the style by an insect, the style flicks downwards, striking the insect pollinator and releasing pollen from the anther in a single dusty mass. However, the breeding systems of blue-flowered Conospermum have not previously been well explored. Flowers on a C. eatoniae inflorescence opened from the basal end upwards acropetally, with the terminal two or three buds never opening. Fruit and seed set occurred only from the basal one to three buds. Isolation of C. eatoniae and C. amoenum flowers showed they were unable to self-pollinate in the absence of insect pollinators. Experiments to determine the timing of the peak of stigmatic receptiveness were inconclusive. Pollen germinated and penetrated the stigma 0 ¡V 6 days after anther dehiscence. Pollen loads on the stigma did not relate to the number of pollen tubes observed down the style. Controlled pollinations of cultivated C. eatoniae at a field station using self and cross pollen, revealed compatibility with a range of pollen genotypes, as pollen tubes were observed extending down the style. However, late-acting incompatibility could not be ruled out as controlled crosses failed to set any seed as flowers were shed from the bush. DNA analysis of open pollinated C. eatoniae seed progeny from two plants from a field station and two plants in natural bushland revealed very different pollination habits. Plants from the field station showed no outcrossing, with progeny closely resembling the maternal parent, whereas plants from the wild population showed outcrossing with several different paternal parents. These results suggest self-pollinated seed can be reliably obtained in a plantation situation using stands of ramets of the same clone. Alternatively, assuming that the required insect pollinators are present in a cultivated stand, it should be possible to obtain cross pollinated seed by surrounding the maternal plant with the desired paternal parent. Unusual pollen behaviour was observed for many blue-flowered species, a white-flowered species of Conospermum, and close relative, Synaphea petiolaris. Up to three pollen tubes emerged from the triporate pollen in vitro, and at rates of up to 55 ƒÝms-1. This rate was maintained for only 2 s but is greater than 20 times faster than reported in the literature for any species, in vitro or in vivo. Pollen with multiple tubes was also observed on the stigma in vivo in C. amoenum flowers. Changing the osmotic pressure of the germination medium by altering sucrose concentration influenced the number of tubes to emerge from the pollen grain; generally the number of tubes decreased as sucrose increased. However, the rate of tube growth was unaffected. The addition of calcium channel blockers to the germination medium had no effect on Conospermum growth rate, nor did they eliminate pulses of tube growth. Observation of Conospermum pollen ultrastructure revealed similarities to Gramineae pollen. The tube cytoplasm was packed with vesicles filled with material of similar electron density to the cell wall. Few golgi were identified, and the apical end of the tube contained these vesicles, smaller secretory vesicles and mitochondria. This is atypical of the tip, which is normally free of large vesicles. Distinct zones in the cytoplasm were not identified, which is similar to Gramineae. Like the grasses, Conospermum appears to pre-manufacture cell wall material and store it in vesicles ready for rapid germination and extension. A biological function of multiple pollen tube emergence with such rapid growth was not elucidated. This research has shown Conospermum to be a complex and very interesting genus. Further investigation into the remarkable growth of multiple pollen tubes would enhance our knowledge of the biological processes involved in tube growth and the process of fast wall formation. The potential benefits to the cut flower industry of commercialising some of these species warrants further effort to find an efficient method of propagation. Introduction into horticulture may be the only means by which these threatened species will survive.

No description available.

Thesis (Ph. D.)--University of Adelaide, Dept. of Horticulture, viticulture and ocnology, 1996. / Copy of author's previously published article inserted. Includes bibliographical references (leaves 127-154).

Thesis (Ph. D.)--Washington State University, December 2008. / Title from PDF title page (viewed on Jan. 22, 2009). "School of Biological Sciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 4, 2009) Vita. Includes bibliographical references.

Hybridization within Sorghum bicolor (L.) Moench has been the primary means of creating genetic diversity needed for sorghum crop improvement. While significant variation exists within S. bicolor, there are several traits that can be improved and potential opportunities to improve S. bicolor if secondary and tertiary germplasm pools could be accessed. Recently, the discovery of the iap (Inhibition of Alien Pollen) mutant and its introgression into more breeding-amenable genetic background has facilitated the development of S. bicolor germplasm with genetic diversity not previously seen within Sorghum. The key to producing this variation is the homozygous recessive mutant gene iap which removes an important reproductive isolation barrier to hybridization. Development of a S. bicolor accession (Tx3361) containing the mutant allele iap and ms3 has allowed introgression of genomic regions from divergent sorghum species into S. bicolor. Given the success with divergent sorghum species, there is a real interest in assessing the potential of this mutant to facilitate intergeneric hybridization. The objective of this study was to determine the range and effectiveness of the iap mutant to allow pollen tubes of Poaceae species outside of the genus Sorghum to grow into S. bicolor pistils. Accessions from the genera Zea, Miscanthus, Pennisetum, and Sorghastrum were used as pollen donors onto Tx3361 and fluorescent microscopy was used to determine the distance through the pistils that foreign pollen tubes grew. Results indicate high levels of pollen tube growth into the ovaries of S. bicolor pistils for two accessions of Pennisetum ciliare (L.) Link and four accessions of Zea mays L. Pollen tubes of other accessions tested did grow to the ovary but in very small numbers. While the recovery of embryos was not attempted in this study, the results indicate that there is potential for hybridization, but the specific pollinator within a species is critical in this attempt.

Switchgrass (Panicum virgatum L.) is a warm-season perennial bunchgrass native to North America. In addition to its importance as a forage grass, it has promise as a biofuel crop. However, its use is limited because the grass is difficult to establish. Improving seedling vigor is one approach for improving establishment. The objectives of this study were to: 1) select for increased seedling mass through half-sib family selection; 2) calculate an estimate of heritability for seedling mass; and 3) determine the mode of pollination of switchgrass. One cycle of selection was completed using a half-sib methodology. Seedling mass was determined in a series of growth chamber studies. The seed was produced in different space planted field nurseries in the College Station, TX area. Mean seedling weight of the base population (C0) was 0.014 gm seedling-1, while the mean seedling weight from the C1 cycle of selection was 0.029 gm seedling-1. Unfortunately, bulked seed from the base population was old and did not germinate well. Therefore, a new base population was recreated, and the C0 seedlings from this population were heavier than the C1 seedlings, 0.020 and 0.016 gm seedling-1, respectively. The calculated heritability estimate was H2 = 0.6. Since the C0 and C1 nurseries were not grown on the same soil type, the lack of a positive response for seedling weight may be due to the different soil types. However, it may require another cycle of selection to determine if seedling mass can be positively impacted via half-sib selection. The mode of pollination of the species was determined by 1) observing pollen germination and tube growth in the pistils using fluorescent microscopy and 2) determining seed set with selfed plants. When self-pollinated, the pollen tubes never grew into the ovaries but when cross-pollinated the tubes readily grew to the micropyle. Also, when switchgrass plants were self-pollinated, viable seed were not produced. These findings indicate that switchgrass is highly self-sterile because a self-incompatibility mechanism prevents the pollen tubes from growing into the ovary of the same genotype.

Copy of author's previously published article inserted. Bibliography: leaves 127-154. Pollination and fruit development were investigated in relation to abscission and abnormalities, specifically, blanking, semi-blanking, non-splitting and premature splitting of fruit. Pollen germination was assessed in Pistacia vera, P. atlantica and P. terebinthus. The pollen tube pathway in pistachio was documented precisely. Growth periods of normal and abnormal pistachio fruits were investigated.

Copy of author's previously published article inserted. / Bibliography: leaves 127-154. / xiv, 155 leaves, [19] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Pollination and fruit development were investigated in relation to abscission and abnormalities, specifically, blanking, semi-blanking, non-splitting and premature splitting of fruit. Pollen germination was assessed in Pistacia vera, P. atlantica and P. terebinthus. The pollen tube pathway in pistachio was documented precisely. Growth periods of normal and abnormal pistachio fruits were investigated. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Ocnology, Waite Agricultural Research Institute, 1996