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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School


First Advisor

George W. Buchenau


Fungal populations within soybean plants, and the effects of benomyl and metalaxyl upon these, were monitored over 1984, 1985, and 1986 in a field having a history of moderate Fusarium root rot of soybean. Both F. oxysporum and P. ultimum were present in asymptomatic field-grown soybean plants. Pythium spp . endophytes (including P. ultimum, P. irrequlare, P. dissotochum, P. acanthicum, and two Pythium spp. 'group HS') were most numerous in early seedling development, and were gradually replaced by endophytic F. oxysporum populations. Benomyl and metalaxyl reduced endophytic populations in some cases, but did not eliminate them. In greenhouse studies, low soil moisture encouraged Fusarium root rot, P. ultimum root rot and the two diseases combined. Disease due to both pathogens combined was more severe in cool soils, whereas Pythium root rot severity increased with soil temperature. Synergism was indicated between P. ultimum and F. oxysporum and also F. eguiseti in soybean disease.

Library of Congress Subject Headings

Soybean -- Diseases and pests -- South Dakota
Fusarium oxysporum
Pythium ultimum
Root rots



Number of Pages



South Dakota State University