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Disease Detection and Losses

Effect of Plant Age at Time of Inoculation with Maize Dwarf Mosaic Virus on Disease Development and Yield in Corn. Eugen Rosenkranz, Plant Science Laboratory, Federal Research, Science and Education Administration, U.S. Department of Agriculture and Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State, MS 39762; Gene E. Scott, Plant Science Laboratory, Federal Research, Science and Education Administration, U.S. Department of Agriculture, and Department of Agronomy, Mississippi State University, Mississippi State, MS 39762. Phytopathology 68:1688-1692. Accepted for publication 23 May 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1688.

When corn (Zea mays) plants of two susceptible hybrids were manually inoculated with maize dwarf mosaic virus strain A (MDMV-A) in the three-, five-, seven-, nine-, and 11-leaf stages during two growing seasons, the highest disease incidence (58%) and the greatest yield reduction (23%) were obtained in plants inoculated at the five-leaf stage. There was no significant difference in disease incidence or in yield reduction between plants inoculated in the three-leaf stage and those inoculated in the seven-leaf stage when data for the two hybrids were combined. Both sets of plants were 47-50% diseased and showed a yield reduction of 15-16%. A delay in inoculation until the 11-leaf stage resulted in a disease incidence one-half as great and a yield reduction one-third as great as those obtained for plants inoculated in the five-leaf stage. Groups of plants inoculated at different stages showed no significant difference in plant height. The average height reduction in all inoculated plants of both hybrids in the 2 yr amounted to 5.4%. Calculations of extrapolated yields for a hypothetical 100% infection rate revealed that yield losses would be surprisingly uniform (36% on the average) for plants inoculated between the three-leaf and the 11-leaf stages. Under particularly favorable conditions for infection and disease development, MDMV-A has the potential for reducing grain yield in a highly susceptible hybrid by as much as 45%.