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Maize Dwarf Mosaic Virus Infection in Susceptible and Resistant Corn: Virus Multiplication, Free Amino Acid Concentrations, and Symptom Severity. J. C. Tu, Postdoctoral Research Associate, Department of Botany and Plant Pathology, Iowa State University, Ames 50010, Present address of senior author: University of Alberta, Edmonton, Alberta, Canada; R. E. Ford, Professor, Department of Botany and Plant Pathology, Iowa State University, Ames 50010. Phytopathology 60:1605-1608. Accepted for publication 4 June 1970. DOI: 10.1094/Phyto-60-1605.

We measured changes in free amino acid (AA) concentrations in inoculated and newly emerged leaves of Illinois-A (Ill-A = resistant) and in inoculated and newly emerged systemically infected leaves of Seneca Chief (SC = susceptible) corn infected with maize dwarf mosaic virus strain A (MDMV-A). MDMV-A can multiply only in inoculated leaves of Ill-A corn. MDMV-A can multiply both in inoculated and newly emerged (systemic) leaves of SC corn. Generally, free AAs increased in MDMV-infected inoculated leaves of both Ill-A and SC corn, but the increased AA concentration in newly emerged leaves was significant only in SC, in which systemic virus movement occurred. The dilution end point of MDMV in inoculated leaves at sampling time was the same for both varieties. No infectivity was detected by assay of newly emerged leaves of the Ill-A corn. Older healthy corn leaves always contained less of each of the respective free AAs than younger ones (12% in SC, 13% in Ill-A), and the difference was narrower after MDMV infection (11% in SC, 4% in Ill-A). SC consistently contained less of each of the respective free AAs than Ill-A in healthy leaves (32% in old, 33% in young leaves) as well as in MDMV-infected ones, although the margin of difference was narrower (25% in inoculated [= older], 19% in systemically infected [= younger] leaves). Mosaic symptoms are not induced by an imbalance of free amino acids and/or virus multiplication in mature leaves with mature chloroplasts.