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Maize Dwarf Mosaic Virus Increases Susceptibility of Sorghum and Corn to Helminthosporium maydis Race T. S. P. S. Beniwal, Former Graduate Research Assistant, Department of Botany and Microbiology, Auburn University Agricultural Experiment Station, Auburn, Alabama 36830, Present address of senior author: Assistant Professor, Department of Plant Pathology, G. B. Pant University, Pantnagar, U. P., India; Robert T. Gudauskas, Professor, Department of Botany and Microbiology, Auburn University Agricultural Experiment Station, Auburn, Alabama 36830. Phytopathology 64:1197-1201. Accepted for publication 12 April 1974. DOI: 10.1094/Phyto-64-1197.

Sorghum and corn plants infected with maize dwarf mosaic virus (MDMV) were more susceptible to infection by Helminthosporium maydis race T than those not infected by the virus. The fungus produced large, necrotic and often concentric lesions on leaves of MDMV-infected sorghum; lesions on virus-free plants remained small. Lesions caused by H. maydis on leaves of MDMV-infected corn, N-and T-cytoplasm, were larger and developed more rapidly than on virus-free plants. Sporulation in lesions on MDMV-infected sorghum and corn began earlier and was more abundant than on virus-free plants. Lesions similar to those resulting from infection by H. maydis developed on MDMV-infected sorghum leaves sprayed with H. maydis culture filtrate; very small necrotic lesions developed on virus-free plants. The culture filtrate caused greater water-soaking of MDMV-infected corn leaf sections than of virus-free sections. Increased susceptibility of sorghum to H. maydis race T appeared to be host-dependent, since only five of sixteen hybrids tested showed a positive association between MDMV infection and H. maydis susceptibility.