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Concentration of Maize Dwarf Mosaic Virus in Susceptible and Resistant Corn Hybrids. R. K. Jones, Instructor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061, Present address of senior author: Plant Pathology Department, North Carolina State University, Raleigh 27607; S. A. Tolin, Assistant Professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Phytopathology 62:640-644. Accepted for publication 13 October 1971. DOI: 10.1094/Phyto-62-640.

The concentration of maize dwarf mosaic virus (MDMV), assayed by analytical sucrose density-gradient centrifugation of clarified sap, varied with time after inoculation, leaf position, environmental conditions, and the corn hybrid used as the host. In the susceptible hybrid, Hy × C103, which was grown in the greenhouse, MDMV concentration was 20-25 µg/g fresh wt from 9 through 18 days after inoculation and declined gradually thereafter. Susceptible Golden Cross Bantam grown under the same conditions contained 20-25 µg MDMV/g from day 7 through day 10, but almost no virus after 10 days. Virus concentration in field-grown Hy × C103 and DeKalb 805A, mechanically inoculated with an artistís airbrush, reached a maximum of over 40 µg/g in 4-5 weeks after inoculation, and remained above 20 µg/g for 6-12 weeks. A resistant corn hybrid, T8 × 07B, showed systemic mosaic symptoms when grown in the greenhouse in the winter, but symptoms initially appeared 5-6 days later than in susceptible hybrids. Virus concentration in T8 × 07B ca. 10 days after inoculation was equivalent to that in the susceptible corn. During the summer, in both the greenhouse and field, T8 × 07B showed only occasional longitudinal bands of chlorotic tissue in otherwise normal, dark green leaves. A high concentration of MDMV was extracted from the chlorotic bands but not from the dark green part of the same leaves. The results suggest that the mechanism of resistance in T8 × 07B is not against virus infection or multiplication, but is against movement of the virus in the host.

Additional keywords: Zea mays.