Thesis (Ph. D.)--University of Wisconsin--Madison, 1953. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 50-51).

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin-Madison, 1952. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. Vita. Includes bibliographical references.

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

Motile zoospores of P. dissotocum and P. catenulatum were added to 20 and 60 mesh silica sand and a sandy loam soil to investigate the duration of motility. Both Pythium species remained motile for up to 24 hours in all soil textures tested. However, the duration and percentage of the motile population varied depending upon the soil type and species tested. The duration of survival of motile and encysted zoospores of P. dissotocum and P. catenulatum in air dried and saturated sterile silica sand was also tested. P. dissotocum, under air dried conditions, did not survive while P. catenulatum was capable of surviving 4 and 16 days as motile and encysted zoospores, respectively. Both fungi could be recovered at high percentages after 5 weeks under saturated conditions. The survival structure is believed to be in the form of a zoospore cyst.

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The research is focused on soil factors which can affect <i>Pythium ultimum</i> and the bio control properties of <i>Pseudomonas fluorescens </i>and <i>Bacillus subtilis.  </i>Similar studies have previously been carried out with results that were not always consistent.  One possible explanation was the occurrence of water flow which can influence the location of antagonist bacteria in the rhizosphere, and thus their competitive action.  The innovative point of the work was to design a watering method which minimised the possibility of unwanted water flow.  Three soil factors were considered:  pH (from 5 to 8), temperature (several regimes between 3 and 25°C) and matric potentials (-10, -100, -300 kPa).  Their effect on microbial survival and activity was studied by measuring root colonisation, activity and biocontrol of the antagonistic bacteria.  <i>Bacillus subtilis</i> did not show antagonistic activity against <i>Pythium ultimum</i> and its colonisation was not affected by any soil factors investigated.  No soil pH effect was found on the biocontrol activity of <i>Pseudomonas fluorescens.  </i>The root colonisation of <i>P. fluorescens </i>decreased with increasing temperature and at extreme low matric potential (<-300 kPa).  However, between -120 and -140 kPa this bacterium reached its highest level of root colonisation and its greatest antagonistic activity.  Under such conditions colonisation data showed that there was downward movement of <i>P. fluorescens </i>which could be explained most likely by nematodes as possible vectors.  These results were further investigated during a field test in which using minor doses of antagonistic bacteria no effect of biocontrol treatment against damping off was measured.  A distinct study was carried out on forecasting the time to crop emergence from a model of sugar beet emergence with a measured and/or simulated set of data.