Thesis (Ph. D. - Plant Pathology)--University of Arizona. / Includes bibliographical references.

Thesis (M.S.)--Youngstown State University, 2008. / Includes bibliographical references (leaves 40-43). Also available via the World Wide Web in PDF format.

Thesis (M.S.)--Youngstown State University, 2008. / Includes bibliographical references (leaves 66-68). Also available via the World Wide Web in PDF format.

Proefschrift--Utrecht. / "Summary and conclusions": p. 131-135. "Litteratuur": p. 142-157.

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 44.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Inoculation experiments were carried out to determine the relation between bark moisture level of certain host species and their susceptibility to facultative parasites. In these experiments, cuttings of 1-to 3-year old host material and the mycelial mat of the pathogens contained in an agar cylinder were used. In the first instance, fungi that were known or found in association with bark lesions were considered: these were Cryptodiaporthe salicella (Fr.) Petrak on Salix scouleriana Barratt (Scouler willow), Dactylosporium sp. and Fusarium sp. on Acer macrophyllum Pursh. (broadleaf maple, Libertella sp. on Cornus stolonifera (Michx.) var. occidentalis (T. and G.) C. L. Hitchc. (western dogwood), Melanconis sp. on Alnus rubra Bong. (red alder). The results demonstrated that fungi normally associated with lesions of living host material proved to be pathogenic when the relative turgidity of the host bark was lowered from the field level of above 80 per cent to the range of 69 to 77 per cent. Secondly, an attempt was made to determine if correlation existed between bark moisture level and canker development by fungi not known, and not found to occur in association with lesions of some hosts. The following fungi and hosts were considered: C. salicella on red alder (Alnus rubra Bong), trembling aspen (Populus tremuloides Michx.), bitter cherry (Prunus emarginata Dougl.), black cottonwood (Populus trichocarpa Torrey and Gray), western dogwood (Cornus stolonifera var. occidentalis), and on broadleaf maple (Acer macrophyllum Pursh.); Fusarium sp. on red alder, bitter cherry, western dogwood, and on Scouler willow; Libertella sp. on red alder, bitter cherry, broadleaf maple, and on Scouler willow; Melanconis sp. on bitter cherry, western dogwood, broadleaf maple and on Scouler willow. It was shown that all of these parasites extended their host ranges, to varying extent when the bark moisture level was reduced to levels within the range of 69 to 77 per cent, or in some instances to the range of 41 to 67 per cent of saturation. Cuttings with as low bark moisture levels as 41 per cent appeared to be viable as indicated by the production of roots and (or) shoots. / Science, Faculty of / Botany, Department of / Graduate

No description available.

No description available.

Phytophthora parasitica, P. citrophthora, and other plant pathogenic fungi were isolated from re-cycled water used to irrigate citrus and other crops. The several propogules of P. parasitica were then studied to determine their survival capabilities in soil and irrigation water. Chlamydospores of P. parasitica were present in field soils from foot-rot infested citrus groves and persisted for at least 60 days in air-dried or moist soils. They germinated in irrigation water or moist soil and formed sporangia within 16 hr. Sporangia were also present in these field soils and survived for at least 60 days in moist soil. They germinated, releasing zoospores into irrigation water 5 min after being inundated. Zoospores were not present in water flooded on air-dried field soil until after 20 hr incubation. Citrus leaves became infected by zoospores within 15 min when placed in zoospore infested water. Although they remained motile in irrigation water for up to 20 hr at 20 C, zoospores encysted when agitated or upon the addition of nutrients, orange peel, or citrus leaves. At low nutrient levels (< 5 mg glucose/liter of sterile distilled water) zoospores germinated and upon cessation of growth the protoplasm contracted within the hyphae and pseudo-septa were formed. Empty cysts or hyphae often lysed; remaining hyphal fragments containing protoplasm survived for at least 40 days at 25 C in untreated waste water and resumed growth upon addition of nutrients. At higher nutrient levels (10-1,000 mg glucose/liter of sterile distilled water) the hyphal tips often produced appressorium-like structures when in contact with the container surface. Exudates from orange peel or citrus leaves stimulated similar activity. The appressorium-like structures usually germinated to produce microsporangia when the nutrients were replaced with untreated irrigation waste water. Some microsporangia persisted in untreated waste water at 25 C for 60 days but most germinated sooner, producing only a single zoospore. Mycelial inoculum from these zoospores was pathogenic to roots of citrus seedlings. Results indicate that P. parasitica is spread by re-cycled irrigation water and that zoospores, or structures produced by them, can play a significant role as survival or dispersal units in re-cycled water.