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Maize Dwarf Mosaic Virus Predisposes Corn to Root Rot Infection. J. C. Tu, Former Postdoctoral Research Associate, Department of Botany and Plant Pathology, Iowa State University, Ames 50010, Present address of senior author: Electron Microscope Laboratory, Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada; R. E. Ford, Professor, Department of Botany and Plant Pathology, Iowa State University, Ames 50010. Phytopathology 61:800-803. Accepted for publication 11 February 1971. DOI: 10.1094/Phyto-61-800.

Corn seedlings infected with maize dwarf mosaic virus (MDMV) were more susceptible to root rot diseases incited by Gibberella zeae and Helminthosporium pedicellatum than were virus-free ones. Root rot was most severe in MDMV-diseased corn seedlings at high densities of fungus inoculum. The difference in root rot severity between MDMV- and non-MDMV-diseased corn seedlings was less in soil with high levels of inoculum. Higher concentrations of carbohydrates and nin-hydrin-positive substances were found in culture solutions around MDMV-diseased corn roots than around virus-free roots. Culture solutions from liquid culture of MDMV-infected plants supported more fungal and bacterial growth than those from virus-free plants. Weakening of the host due to MDMV infection and increasing inoculum potential due to more root leakage probably are directly associated with more severe root rot disease in MDMV-infected than virus-free corn.