Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The interaction of soybean cultivars (Glycine max) with Phytophthora megasperma f.sp. glycinea (Pmg) races is governed by single host genes (Rps) and is consistent with the "gene-for-gene" hypothesis. Using the near isogenic cultivars Harosoy ({dollar}rps\sb1{dollar}, susceptible to race 1) and Harosoy 63 ({dollar}Rps\sb1{dollar}, resistant) and Pmg race 1 it was demonstrated that the {dollar}Rps\sb1{dollar} gene is expressed in hypocotyls and roots of light and dark grown seedlings, in green cotyledons and leaves but not in immature leaves. Leaves of cv. Harosoy became resistant with age. The phytoalexins, glyceollin isomers I, II and III, accumulated rapidly in resistant responses. Proportions of the glyceollin isomers varied with the organ, exposure to light, interaction type and incubation period. The three isomers, also differed in their toxicities to Pmg. Glyceollin I was almost twice as inhibitory as glyceollin II and III to mycelial growth in vitro. An isolate of Pmg race 1 (Isolate 1.1) was obtained that was twice as tolerant to glyceollin I and III as race 1. Evidence was obtained for variability in morphology, growth, tolerance to glyceollin I and aggressiveness of single-zoospore progeny of race 1 and Isolate 1.1, that may be accounted for by cytoplasmic factors.;From pulse and pulse-chase experiments using L- (U{dollar}\sp{lcub}14{rcub}{dollar}C) -phenylalanine as precursor it is concluded that accumulation of higher levels of glyceollin I in resistant than in susceptible responses is due to differences in rates of biosynthesis. Rapid metabolism, which was not constitutive, was demonstrated in all interactions and controls. This is consistent with differences in phenylalanine ammonia-lyase (PAL) activity demonstrated in resistant and susceptible responses. PAL activity also was correlated with changes in glyceollin production and susceptibility at elevated temperatures. Differential effects of temperature on growth and glyceollin I sensitivity of Pmg races were demonstrated also. In some race-cultivar combinations reaction types may be related to the effect of temperature on production and sensitivity to glyceollin I.;A model is presented that attempts to accommodate the physiological data obtained in this study with the requirements of the "gene-for-gene" relationship of host-pathogen interactions.



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.