No description available.

No description available.

No description available.

Doctor of Philosophy / Department of Plant Pathology / Harold N. Trick / Bread wheat (Triticum aestivum L.) is an important staple crop for 35% of the world’s population. One economically important pathogen of wheat is Puccinia triticina, the causal agent of leaf rust, can cause up to 50% yield loss during epidemics. Despite the lack of an alternate host to complete the sexual stages, P. triticina still has variation within the population, which can make achieving durable resistance difficult. This study aims to gain a better understanding of the P. triticina-wheat interaction by identifying wheat genes that are induced by individual and multiple races. Six P. triticina races were evaluated on a susceptible variety of wheat at six days post inoculation. RNA was sequenced and 63 wheat genes were identified that showed varying expression in response to the six P. triticina races. Fifty-four wheat genes were characterized during the first seven days of infection using real-time PCR. Race specific gene expression was found in three wheat genes with race differences on Lr2A, Lr2C, and Lr17A. Wheat genes that had similar expression in response to all six races were also identified. Seven of the characterized genes were then silenced using RNAi hairpin constructs. The transgenic plants were molecularly characterized and inoculated with a virulent P. triticina race in the T₂ generation. However, the endogenous genes were not silenced and the transgenic plants maintained susceptibility. A mutation approach was also used to identify wheat genes involved in infection. A mutant population of 3780 wheat plants was created using EMS. Fifteen hundred mutants from the M1 population were screened for plants with a different infection phenotype compared to the non-mutated control and 570 were selected. After two additional generations of selection, eight resistant mutants were obtained. The gene expression of the seven previously identified genes were evaluated and one mutant showed reduced expression of an ER molecular chaperone gene. This research uses a forward and reverse genetics approach to identify and evaluate the function of wheat genes in the wheat-P. triticina interaction. Although RNAi could not determine the gene function, the knockout mutant shows that the identified genes may have a crucial role in infection.

Wheat (Triticum aestivum L. em. Thell, 2n=6x=42, AABBDD) is subjected to significant yield losses by the endemic leaf rust pathogen, Puccinia triticina (Roberge ex Desmaz. F. sp. tritici). Breeding for resistance to this disease is a more appropriate option both environmentally and economically over fungicidal application. More than 57 leaf rust resistance genes in wheat have been identified and many of the resistance genes have been successfully introgressed into resistant cultivars, yet the continuous shifting of predominant races of P. triticina continues to be a challenge to breeders. Pyramiding multiple resistance genes into a single resistant cultivar is one of the preferred strategies to develop superior disease resistant cultivars. Efficient pyramiding requires the utilization of markers closely linked to the resistance genes. The objectives of this study were to characterize a novel source of resistance to leaf rust introgressed into the breeding line WX93D180-R-8-1, to determine its inheritance, map position, and linkage with molecular markers suitable for marker assisted selection. According to the pedigree of WX93D180, TX86D1310*3/TTCC417, the resistance in this breeding line should be derived from TTCC417 (Turkey tritici cereal collection), which was thought to be Triticum monococcum, which is a diploid species made up of only the A genome. However, our marker analyzes results indicated the resistance gene is located in the D genome and has the same location as the cloned leaf rust resistance gene Lr21. We verified the result in our population using primers from Lr21 and found the same segregation pattern with the phenotypic data (disease response). Therefore the pedigree is incorrect, TTCC417 was misidentified, or the resistance was not from TTCC417.

The Pteridaceae has been variously classified by different taxonomists. The leaf epidermal morphology of 48 species in 11 genera of Taiwan Pteridaceae was studied using SEM. There are six types of trichomes, two types of adult stomata and three types of epidermal morphology described. And the variability of some epidermal characters, such as the stomata flush or sunken, the long axes of epidermis cell lie parallel to the vein or not, the lines on cells or not, could distinct part of genera and subfamilies. Based on previously described characters, the epidermis pattem of Cheilanthes could be divided into four types, the cheilanthes type, the aleuritopteris type, the mildella type and the doryopteris type; and that of Adiantum could be divided into two types, branched type and nonbrached type. And the epidermis morphology of Coniogramme was very simility to that of Pteris. Besides, the epidermis characters showed that Cryptogramma, Onychium and Acrostichum are unique. And more study of the three genera is needed to understand the relationships among these genera.

Wheat (Triticum aestivum L. em. Thell, 2n=6x=42, AABBDD) is subjected to significant yield losses by the endemic leaf rust pathogen, Puccinia triticina (Roberge ex Desmaz. F. sp. tritici). Breeding for resistance to this disease is a more appropriate option both environmentally and economically over fungicidal application. More than 57 leaf rust resistance genes in wheat have been identified and many of the resistance genes have been successfully introgressed into resistant cultivars, yet the continuous shifting of predominant races of P. triticina continues to be a challenge to breeders. Pyramiding multiple resistance genes into a single resistant cultivar is one of the preferred strategies to develop superior disease resistant cultivars. Efficient pyramiding requires the utilization of markers closely linked to the resistance genes. The objectives of this study were to characterize a novel source of resistance to leaf rust introgressed into the breeding line WX93D180-R-8-1, to determine its inheritance, map position, and linkage with molecular markers suitable for marker assisted selection. According to the pedigree of WX93D180, TX86D1310*3/TTCC417, the resistance in this breeding line should be derived from TTCC417 (Turkey tritici cereal collection), which was thought to be Triticum monococcum, which is a diploid species made up of only the A genome. However, our marker analyzes results indicated the resistance gene is located in the D genome and has the same location as the cloned leaf rust resistance gene Lr21. We verified the result in our population using primers from Lr21 and found the same segregation pattern with the phenotypic data (disease response). Therefore the pedigree is incorrect, TTCC417 was misidentified, or the resistance was not from TTCC417.

Thesis (Ph. D.)--Leland Stanford junior university, 1907. / Cover title. eContent provider-neutral record in process. Description based on print version record.

The effect of foliar applied potassium chloride on Septoria tritici on winter wheat was quantified and possible modes of action investigated by in vitro, glasshouse, controlled environment and field experiments between 1996 and 1999. In vitro experiments showed that as the concentration of potassium chloride increased, mycelial growth and germination of conidia decreased (EO sos of 1.36M and 0.7M, respectively). One glasshouse and two field experiments showed a significant reduction in the leaf area affected by S. trttict after foliar application of potassium chloride compared to untreated controls. In general, application of potassium chloride reduced the leaf area affected by S. tritici by 20 -.40%. However, a significant yield increase was not observed. Potassium chloride applied to the lower leaves of winter wheat did not confer systemic acquired resistance against S. tritici on the upper leaves. Inhibition of conidial germination, on leaf surfaces by potassium chloride was observed. Similar inhibition was observed when polyethylene glycol, an inert osmoticum, was applied at the same calculated osmotic potential. During field experiments there was no significant difference in the leaf area affected by S. tritici in plots treated with potassium chloride or polyethylene glycol, although both significantly reduced the leaf area affected compared to untreated control plots. Therefore, the principal mode of action of potassium chloride was proposed to be as a result of adverse osmotic conditions caused by the salt on leaf surfaces. However, the addition of a range of adjuvants to potassium chloride did not increase the efficacy of S. tritici control in glasshouse studies. The results from this study show that potassium chloride, when applied to foliage of winter wheat can reduce the leaf area affected by S. tritici and it is proposed that this reduction was by adverse osmotic conditions caused by the salt on leaf surfaces.

No description available.