Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Soybean (Glycine max) cultivars interact specifically with avirulent (incompatible) or virulent (compatible) races of Phytophthora megasperma f. sp. glycinea to give resistant or susceptible responses. In a search for factors involved in specificity, advantage was taken of the fact that the resistant interaction between soybean cv Altona and Phytophthora megasperma f. sp. glycinea race 4 becomes susceptible at 32(DEGREES)C thus providing in a single race-cultivar combination differences in interaction type without the uncertainties introduced when comparisons are made between cultivars or races with different genotypes. The effect of temperature was shown to be on the interaction at or subsequent to infection; susceptibility to race 4 developed only when plants were incubated at 32(DEGREES)C after inoculation. The phytoalexin, glyceollin, accumulates in resistant reactions in highly fungitoxic concentrations, but not in susceptible reactions including the temperature-induced susceptible response to race 4 at 32(DEGREES)C. Elicitors from cell walls and culture filtrates of Phytophthora megasperma f. sp. glycinea reportedly stimulate glyceollin production. The effect of incubation temperatures on the production of elictors by the fungus was examined and activity in cotyledon and hypocotyl bioassays was determined. No temperature related differences were found and preparations from the compatible race 6 had similar activity. The abiotic elicitor AgNO(,3) was equally active at both temperatures. Thus, induced susceptibility to race 4 at 32(DEGREES)C was not due to inability to produce elicitors in culture, lack of activity at 32(DEGREES)C, or inability of the host to produce glyceollin at 32(DEGREES)C. Fluids recovered from the intercellular spaces of uninfected and infected soybeans were also examined for the presence of elicitors. No correlations of activity with resistance and temperature-induced susceptibility were found. The protein constituents of intercellular fluids were studied using electrophoresis and high performance liquid chromatography. New proteins not present in controls were detected following infection, and additional changes both in number and amount of proteins were associated with incompatible or compatible interactions. In the same genetic background (cv Altona and race 4), three proteins accumulated in the incompatible interactions and one protein was restricted in occurrence to the temperature-induced compatible interaction. Intercellular fluids also were examined for factors which could induce susceptibility or induce resistance. A constituent(s) from both uninfected and hypocotyls infected with either race interfered with disease development.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.