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Resistance in Soft Red Winter Wheat to Mycosphaerella graminicola. Gregory Shaner, Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Robert E. Finney, research associate, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 72:154-158. Accepted for publication 1 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-154.

Six soft red winter wheat cultivars and four breeding lines that had shown various levels of resistance to speckled leaf blotch in the field were inoculated in the greenhouse with pycnidiospores of Mycosphaerella graminicola. Significant differences were found in both percent leaf area affected and number of pycnidia per square millimeter of lesion among cultivars at all growth stages ranging from pseudostem erection to midmilk. More significant differences among cultivars were detected at the later growth stages. Cultivar Oasis, which derives its resistance to M. graminicola from cultivar Bulgaria 88, was consistently the most resistant, and cultivar Monon was the most susceptible. Several other cultivars became more resistant with age. Fewer pycnidia per unit area of lesion were produced on cultivar Caldwell even though necrotic lesions developed. This suggests that M. graminicola would not spread effectively in pure stands of this cultivar. Several of the resistant cultivars were derived from parents susceptible to speckled leaf blotch, suggesting that their resistance is the result of a combination of genes that individually are ineffective for resistance.