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Development of Maize Dwarf Mosaic Symptoms in Eight Phytotron Environments. D. L. Thompson, Research Agronomist, Crops Research Division, ARS, USDA, North Carolina State University, Raleigh 27607; T. T. Hebert, Professor of Plant Pathology, North Carolina State University, Raleigh 27607. Phytopathology 60:1761-1764. Accepted for publication 6 July 1970. DOI: 10.1094/Phyto-60-1761.

Resistant and susceptible corn plants (Zea mays L.) were grown in eight phytotron-controlled environments, inoculated 14 days after planting with maize dwarf mosaic virus (MDMV), and observed for 31 days for symptom expression. Eighteen plants of 3 resistant entries and 148 plants of 5 susceptible entries developed symptoms. The average number of days between inoculation and symptom expression in the different environments ranged from 18 to 31 days for resistant entries, and from 4.7 to 7.3 days for susceptible entries. A significant reduction in plant height was obtained 6 days after inoculation. The most rapid expression of symptoms occurred at night temperatures of 26 C combined with day temperatures of either 26 or 30 C. Per cent plants infected and time required to show mosaic symptoms were more closely correlated with night temperatures than with day temperatures. Varied responses among resistant entries suggest that a range of evaluation environments might prove useful for identifying strains having maximum resistance.