Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Plant Breeding" Title from author supplied metadata (record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Thesis (M. S.)--Texas A&M University, 2006. / "Major Subject: Plant Breeding" Title from author supplied metadata (automated record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Plant Breeding" Title from author supplied metadata (automated record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A & M University, 2003. / "Major Subject: Plant Breeding." Title from author supplied metadata (automated record created on Apr. 30, 2004.). Vita. Abstract. Includes bibliographical references.

Thesis (M.S.)--Texas A & M University, 2003. / "Major Subject: Plant Breeding." Title from author supplied metadata (automated record created on Apr. 30, 2004.). Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A & M University, 2003. / "Major Subject: Plant Breeding." Title from author supplied metadata. Includes bibliographical references.

Models are developed for the evolution of outcrossing in general and the evolution of distyly in particular. Field studies of distylous Lithospermum cobrense (Boraginaceae) are reported to support and compliment theoretical work. First a method is developed to model selection against selfing which takes into account the effects of consecutive generations of selfing on loss of heterozygosity. Conditions are then derived for optimal rates of outcrossing. Intermediate rates of outcrossing are optimal under a wide range of parameter values. One assumption of this model is that seedset is not pollen-limited. I then investigate the nature of inherent constraints on whether seedset is pollen-limited or resource-limited in outcrossing animal-pollinated plants, and conclude resource limitation is likely when the per-seed cost of fruit production is greater than the per-seed cost of pollen production. The model also points to why animal-pollinated plants usually have hermaphrodite flowers. This model is followed by analyses of pathways for the evolution of self-incompatibility with two mating types such as is associated with distyly. To account for this I show it necessary to postulate a fortuitous conjunction of rare mutations, very severe selection against selfing, and/or unusual mutational effects. It is also necessary to postulate resource-limited seedset. At this point I develop models for floral differentiation of mating types, culminating in the completely distylous condition. Once self-incompatibility has evolved in plants with stigmas and anthers already spatially separated, it is possible to account for complete floral differentiation under both pollen limitation and resource limitation. Field studies of L. cobrense focus on the pattern of pollen dispersal by butterflies, the mechanism accounting for this pattern, and the extent to which this pattern leads to resource or pollen limitation of seedset. In this species and in distylous species generally, the major effect of reciprocal placement of anthers and stigmas in the two mating types is to enhance the efficiency with which pollen is transported to compatible stigmas. This enhances male fitness but for full distyly to evolve it is helpful, though not strictly necessary, for female fitness to be affected too, as under pollen limitation. Finally, I argue that sporophytically controlled multiallelic self-incompatibility may originate by pathways similar to those envisioned for distyly, and that these two kinds of breeding systems are branches with a common stem.

A diversity of plants ranging from completely rosette types to completely floral types can be found during the seedling year in Dollard red clover. Bird (1948) described five plant types (called 0, 1, 2, 3, and 4) based on the degree of floral stem development in the year of establishment. [...]

No description available.

Septoria tritici blotch (Stb) is a major foliar disease of wheat worldwide caused by the fungal pathogen Mycosphaerella graminicola. This project mapped the chromosomal locations of Stb resistance, which will be useful for wheat cultivar enhancement. In the first study of this project, Stb resistance and grain yield quantitative trait loci (QTL) were identified in a winter wheat doubled-haploid (DH) population produced from the cultivars Pastiche (resistant) and Torfrida (susceptible). A genetic map of the population was constructed using 104 microsatellite and 202 DArT markers. Separate disease and yield field trials were conducted in north-western Europe to measure natural Stb infection and grain yield, respectively. A resistance QTL from Pastiche was identified (QStb.jic-2A) that reduced flag leaf pycnidial density by 31.2% compared to the population mean. A second QTL from Pastiche (QYld.jic-2A) co-localized with QStb.jic-2A, and conferred an increase in grain yield of approximately 2.0% (0.19 t ha-1). The second study determined the map location of the third multiple-isolate resistance gene in the hexaploid landrace Salamouni. A population was developed using the resistant DH line 98S05B*13 (Salamouni/Katepwa) crossed to the susceptible cultivar Katepwa. The parent 98S05B*13 was found to contain the resistance gene Stb14 on chromosome 3BS, therefore, to minimize the effect of this gene, individual plants of the F2 population were selected for self-pollination based on presence or absence of Stb14 using flanking microsatellite markers. The Stb14(+) F2:3 families were screened with M. graminicola isolate MG96-36. Bulked segregant analysis identified a possible linkage to the gene of interest on chromosome 3AS. Polymorphic microsatellite markers on 3AS were used to construct a linkage group. The markers barc321 and barc12 were found to flank the resistance gene at genetic distances of 1.9 and 2.5 cM, respectively. This position on 3AS has not been previously linked to Stb resistance and this gene will be designated StbSm3. The third population was developed to fine map the isolate-specific resistance gene Stb14 located on chromosome 3B of Salamouni. A large population of 84 fixed recombinant F4 families was developed using the co-dominant microsatellite markers flanking Stb14. Attempts to identify clearly polymorphic molecular markers within the interval containing Stb14 were unsuccessful.