published_or_final_version / Botany / Master / Master of Science

Thesis (Ph. D.)--University of Wisconsin--Madison, 1940. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 56-58).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed Oct. 10, 2007). PDF text: xii, 199 p. : ill. (some col.) UMI publication number: AAT 3258408. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (M. Sc.)--University of Hong Kong, 1969. / Typewritten.

Thesis--Ph. D., University of Hong Kong. / Typewritten.

Thesis (M. Sc.)--University of Hong Kong, 1974. / Typescript.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

Ramets of 14 clones of western black cottonwood Populus trichocarpa Torr. & Gray collected from the interior and coast of British Columbia were tested in the nursery for their growth performance after infection by the leaf rust Melampsora occidentalis Jacks. Linear relationships were demonstrated between various growth parameters (total dry weight, stem dry weight, root dry weight, volume, diameter and height) and disease severity rated as diseased leaf-weeks divided by total leaf-weeks. Losses due to rust infection included reduced total dry weight and volume growth in the year of heavy disease, the death of severely infected ramets during the following winter and reduced initial volume increment in the following growing season. The percentage reduction in yield (total dry weight) was greater than the cumulative percent leaf area infected, suggesting that the rust infected leaf parts act as sinks for photosynthate. The normal pattern of photosynthate allocation was altered in favour of the top growth of ramets. Ratios of stem/root dry weight increased rapidly as disease level increased. A threshold infection level, below which no loss occurred, was not detected in this pathosystem. Significant variation in rust resistance of black cottonwood clones was detected both within and between the two geographic areas. Clones from the coast or warm, moist areas were, on average, more resistant than clones from the interior or cold, dry climates. The phenomenon of induced resistance was not detected at either the local or the systemic levels in black cottonwood challenged by the rust. Variation in rust tolerance among black cottonwood clones was demonstrated. Rust tolerance was defined as the slope of the relationship between yield of ramets (expressed as a proportion of controls) and disease severity (expressed as the proportion of the total number of leaf-weeks infected). A negative correlation between rust tolerance and rust resistance was found. In the collection of clones tested, the positive effect of disease resistance on the growth of cottonwood clones was partially counterbalanced by the negative effect of reduced tolerance on the growth. The importance of this relationship in both natural and artificial selection of superior trees against disease is indicated. / Forestry, Faculty of / Graduate

published_or_final_version / Botany / Master / Master of Science

No description available.