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Effect of the Nuclear Genome of Corn on Sensitivity to Helminthosporium maydis race T-toxin and on Susceptibility to H. maydis race T. G. A. Payne, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Laboratory of Agricultural Biochemistry, University of Nebraska, Lincoln, NE 68583; O. C. Yoder, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 68:331-337. Accepted for publication 22 July 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-331.

Differences in susceptibility of corn genotypes (containing Texas male-sterile cytoplasm) to Helminthosporium maydis (Nisikado and Miyake) race T and in sensitivity to H. maydis race T-toxin were determined using quantitative bioassays. Evaluation of a wide range of genotypes indicated that both the level of susceptibility of corn to the fungus and the degree of sensitivity to the toxin were influenced by the nuclear genome. However, differences in susceptibility to the fungus were not correlated with differences in sensitivity to the toxin. Nuclear genes that influence cytoplasmic sensitivity to the toxin appear to play no role in disease development, whereas cytoplasmic sensitivity to toxin is known to cause increased susceptibility to H. maydis race T. These observations, and those of previous studies on the genetics of H. maydis, support the hypothesis that this toxin is not required for the establishment of a compatible host-parasite relationship but that it does contribute to the virulence of H. maydis race T on corn containing Texas male-sterile cytoplasm. This role in disease differs from those that have been described for host-specific toxins produced by several other fungal plant pathogens.

Additional keywords: southern corn leaf blight, host-specific toxin.