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Resistance

Effectiveness of Resistance to Maize Dwarf Mosaic and Maize Chlorotic Dwarf Viruses in Maize. Gene E. Scott, Research agronomist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and also professor, Department of Agronomy, Mississippi State University, Mississippi State 39762; Eugen Rosenkranz, research plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture and professor, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762. Phytopathology 71:937-941. Accepted for publication 21 January 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-937.

Progeny of a 13-parent diallel cross of resistant (R) and susceptible (S) inbred lines of maize (Zea mays) were evaluated for resistance to maize dwarf mosaic virus (MDMV) and maize chlorotic dwarf virus (MCDV) during 2 yr of testing. Inbreds with similar resistance did not necessarily impart equal levels of resistance to their hybrids when crossed to susceptible inbreds. Lines Ab28A and Mp412 contributed the greatest amount of maize dwarf mosaic (MDM) resistance to their hybrids, whereas Mp412 and T232 contributed the greatest amount of maize chlorotic dwarf (MCD) resistance to their hybrids. When the disease incidence of MDM or MCD was high (8590% of susceptible plants diseased), resistance expressed by the R S crosses was close to the midpoint between the R R and S S crosses. However, when the disease incidence was low (3560% of susceptible plants showing symptoms), the same R S crosses reacted to the two viruses similar to the R R crosses. Data on percentage of diseased plants were usually as effective in identifying levels of resistance as was data on disease severity ratings. Regression analysis of data on disease reaction enabled estimation of the amount of reduction in disease incidence and severity as well as the probable gain in yield associated with the replacement of each susceptible inbred parent by a resistant one in a hybrid. Our data indicated a lack of synergistic effect on disease severity in corn between MDMV and MCDV.