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Inheritance of Resistance in Corn (Zea mays) to Gray Leaf Spot. Crystal A. Huff, Research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; J. E. Ayers(2), and R. R. Hill, Jr.(3). (2)Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (3)Research agronomist, Regional Pasture Research Laboratory, USDA, ARS, The Pennsylvania State University, University Park 16802. Phytopathology 78:790-794. Accepted for publication 5 January 1988. 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, 1988. DOI: 10.1094/Phyto-78-790.

All possible crosses (including reciprocals) were made among eight corn inbred lines to study the inheritance of resistance to gray leaf spot caused by Cercospora zeae-maydis. Because of cold injury to the developing seeds of two inbreds, seeds from only 40 of the 56 possible crosses were planted in three-replication tests at two Pennsylvania locations. Entries at one location were planted without tillage into corn debris from the previous several years where adequate levels of natural inoculum of C. zeae-maydis were present. The same entries at the second location were planted without tillage into soybean stubble and were inoculated with a conidial suspension of C. zeae-maydis. Seeds of the inbreds were planted in separate three-replication tests at each location. Area under the disease progress curve (AUDPC) values were calculated for each entry from data collected on three dates as percent leaf area exhibiting symptoms of gray leaf spot. Analysis of variance procedures appropriate to this diallel (Griffing model I) were carried out on the AUDPC with the data from locations combined. General combining ability (GCA) effects were 18 times larger than specific combining ability (SCA) effects indicating that, for this set of inbred lines, additive gene action is more important than nonadditive gene action in controlling resistance to gray leaf spot. Reciprocal effects were significant, but the mean squares were small compared with the mean squares for GCA and SCA. Based on estimated GCA effects, inbreds Pa875, Va59, and B68Ht contributed significantly to resistance. Limited disease development on the inbreds permitted only one estimate of disease severity. A mean separation test supported the ranking of inbreds obtained through the diallel analysis. Based on the results obtained with these inbreds, breeders attempting to accumulate gray leaf spot resistance should use programs that favor additive gene action.

Additional keywords: Cercospora zeae-maydis, horizontal resistance, quantitative genetics, rate-reducing resistance.