Thesis (Ph. D.)--University of Michigan, 1915. / Cover title. "Reprinted from the American journal of botany 2 ... December, 1915." "Contribution 150 from the Botanical department of the University of Michigan." "Literature cited": p. 575-576.

Thesis (Ph. D.)--University of Michigan, 1915. / Cover title. "Reprinted from the American journal of botany 2 ... December, 1915." "Contribution 150 from the Botanical department of the University of Michigan." "Literature cited": p. 575-576.

Diss. (sammanfattning) Uppsala : Univ., 2002. / Härtill 4 uppsatser.

Studies of Saprolegnia infections of fish in British Columbia were made to determine disease causing agents and infection conditions. Saprolegnia diclina Humphrey was the most frequently observed parasite. This fungus reproduced sexually both on fish tissue and hemp seed cultures. No definite isolations of S. parasitica Coker were made although some non-sexually reproducing isolates of a Saprolegnia sp. were found. The validity of the species, S. parasitica, has been examined and questioned on the basis of present identification characteristics. Infection studies using S. diclina as the parasite and fingerling coho (Oncorhynchus kisutch) as the host indicated a distinct correlation between temperature and infection. At normal cool temperatures, e.g., 8° C, no infection occurred; at 9°C or above, some infection resulted. Above 9° C, the rate of infection increased as temperature increased. Temperature was also associated with the time at which infection occurred after inoculation. At 18°C, infection began earlier than at 13 C, Heat-shock treatment tended to reduce the temperature-time effect causing initial infection at 13°and at 18° C to occur almost simultaneously. Cold-shock treatment resulted in some infection. Such treatment, however, did not produce the same immediate infection as heat-shock. Histological studies demonstrated the infection to be concentrated in the host epidermis with fungal hyphae at sites of heaviest infection extending through the dermis and into underlying muscle tissues. / Science, Faculty of / Botany, Department of / Graduate

Pure cultures of Saprolegnia ferax (Gruith) Thuret, Achlya americana Humphrey, and two isolates of Saprolegnia parasitica Coker were grown in a chemically defined medium under controlled conditions of temperature and illumination. Light inhibited growth and oogonium formation rates in S. ferax and A. americana. Light inhibited zoospore germination rates in A. americana and the growth rate of S. parasitica isolate 2-27-59; S. parasitica isolate 6-28-60 was indifferent to light. Neither isolate of S. parasitica formed sexual structures during the experiments. Differences in light reactions and growth rates of these two isolates indicated physiological strain differences. Photoreactivation was demonstrated in S. ferax and both isolates of S. parasitica. Evidence was shown that light caused production of toxic substances in the medium which caused inhibition of growth and sporulation. The blue peroxychromic test for hydrogen peroxide in the medium was negative but apparent catalase activity was demonstrated. Using a simple medium consisting of glucose, soluble starch and yeast extract, white light stimulated vegetative growth in S. ferax and A. americana. A quantitative distribution pattern of oogonium formation was shown. / Ph. D.