VIEW ARTICLE

Disease Detection and Losses

Effectiveness of a Disease Index System in Evaluating Corn for Resistance to Maize Dwarf Mosaic Virus. C. W. Kuhn, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602; T. H. Smith, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602. Phytopathology 67:288-291. Accepted for publication 21 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-288.

A disease index system was developed under greenhouse conditions to evaluate corn for resistance to maize dwarf mosaic virus (MDMV). The maize dwarf mosaic index was based on the percentage of plants that develop symptoms and time of symptom appearance after inoculation. When 550 corn lines were evaluated, three distinct disease categories were observed: resistant, intermediate, and susceptible. Index values were reproducible and significantly different between the categories. More important, the index values were related to incidence of disease and to yield of diseased plants in the field. With resistant corn lines, fewer plants became infected naturally, and yield of individually diseased plants was reduced less than with intermediate or susceptible lines. The relative MDMV infectivity levels in corn hybrids also were related to disease index values. Maize dwarf mosaic virus was detected earliest in susceptible hybrids and was present in higher concentrations than in more resistant hybrids.