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Ear-Rotting Potential of Helminthosporium maydis Race T in Corn. Oscar H. Calvert, Associate Professor of Plant Pathology, University of Missouri Agricultural Experiment Station; Marcus S. Zuber, Research Agronomist, ARS, USDA, and Professor of Agronomy, University of Missouri Agricultural Experiment Station. Phytopathology 63:769-772. Accepted for publication 3 January 1973. DOI: 10.1094/Phyto-63-769.

The ear-rotting potential of Helminthosporium maydis race T was determined by inoculating ears of two separate strains of the ‘Pioneer 3306’ hybrid corn. One strain had male-sterile cytoplasm and the other, normal male-fertile cytoplasm. Inoculum-laden toothpicks were inserted in the base, center, and tip of the ear. Inoculations were made 10, 20, 30, and 40 days after flowering and rated 28 days after inoculation. Ears from plants with T-cytoplasm had more extensive rotting than those from normal cytoplasm plants. Ears inoculated at the center had the greatest amount of rot. Rotting was highest when inoculations were made at 10 and 20 days after flowering, and lower at 30 and 40 days. Kernels next to the lesion were infected, but were not visibly damaged. Certain tissues of corn ears with the T-cytoplasm were much more susceptible to infection than others. Susceptibility decreased with age of the tissues. Since H. maydis race T was shown to be seed-transmitted, the possibility exists that the fungus may be disseminated in infected kernels that are not visibly damaged.