Abstract
Dickson, J. G., R. Syamananda, and A. L. Flangas. (U. Wisconsin, Madison.) The genetic approach to the physiology of parasitism of the corn rust pathogens. Amer. Jour. Bot. 46(8): 614–620. Illus. 1959.—Inbred lines of corn, with known genes conditioning rust reaction to specific clonal and inbred lines of Puccinia sorghi, were used in the study of the physiology of parasitism of the several types of rust reaction. Three different rust reactions incited by 3 lines of the pathogen on the same host and 1 line of the pathogen on several inbred lines of corn, as well as other specific host-pathogen interactions were investigated. The influence of temperature, light, and carbohydrate on the comparative phenotypic expression of rust reaction for several host-pathogen genotypes showed differences in response useful for the study of obligate parasitism and the nature of resistance. Both high and low temperatures changed the rust reaction, necrotic fleck, to uredial development and the reverse, for specific genotype combinations. The nature of available carbohydrate (using excised leaves in the absence of photosynthesis) showed little effect on the differential rust reactions, necrotic fleck and uredial development. The comparative rate and total oxygen uptake for leaves of the same host, uninoculated and inoculated with lines of the pathogen inciting the necrotic-fleck, mesothetic-X and uredial reactions, respectively, indicated significant differences in physiological response for the 3 reaction types. The necrotic-fleck reaction showed initially a high oxygen uptake that subsided with the isolation of the obligate parasite by host-cell necrosis, in contrast to the continuous increase in oxygen uptake in the compatible reaction. The data indicated that in the necrotic-fleck reaction, the fungus line was initially virulent but nonpathogenic rather than avirulent as indicated commonly in the literature. The results showed also that in corn rust, the compatible and the mesothetic-X reactions were differentially selective, whereas the necrotic-fleck was incited uniformly on all resistant host genotypes.
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