Identification of Slow-Rusting Resistance to Puccinia polysora in Maize Inbreds and Single Crosses. B. A. Bailey, Research Assistant, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843. Wolfgang Schuh, R. A. Frederiksen, A. J. Bockholt, and J. D. Smith. Research Assistant, Professor, Department of Plant Pathology and Microbiology, Associate Professor, and Professor, Department of Soil and Crop Science, Texas Agricultural Experiment Station, College Station 77843. Plant Dis. 71:518-521. Accepted for publication 17 December 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0518.

Epiphytotics of southern rust occurred in the southern United States in 1972, 1973, and 1974, raising concern over the relative susceptibility of the maize germ plasm in the United States to Puccinia polysora. Slow rusting is a common form of resistance to many rust diseases, but slow rusting has not been evaluated in the maize / P. polysora interaction. For this reason, tests were designed to evaluate the slow-rusting characters of 23 single crosses and 33 inbreds in 1983 and 1984. The area under the disease progress curve (AUDPC) was calculated for each entry, using weekly assessments of pustule density. Individual weekly assessments of pustule density were also analyzed to compare the relative effectiveness of the two methods for identifying slow rusting. Significant differences were observed among both inbreds and single crosses for AUDPC and for pustule density. The maize inbreds and single crosses evaluated showed considerable variation for the slow-rusting trait. Rank correlations between years were higher for AUDPC than for pustule density, although rank correlations over years between pustule density and AUDPC were all high. The indication is that weekly assessments, if correctly timed, are as effective for identifying slow rusting as AUDPC, although they do not provide the details that can be gained by the multiple assessments used in calculating AUDPC.