Analysis of Symptoms on Spring and Winter Wheat Cultivars Inoculated with Different Isolates ofSeptoria nodorum

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Abstract
Ten winter and spring wheats that differed in level of resistance were quantitatively inoculated with 14 different cultures of S. nodorum. Symptoms measured were the number of lesions per square centimeter and the percentage leaf area necrotic on seedlings. The wheats differed in responses to the single isolates of S. nodorum from uniformly mild (winter wheats ''Anderson'', ''Coker 68-8'' and ''Redchief'') to uniformly severe (spring wheats ''Fortuna'' and ''Polk''). Moderate cultivar .times. isolate interactions were found in the winter wheats ''91-728'', ''Centurk'' and ''Flint'' and in the spring wheat ''Olaf.'' Seedling disease severity agreed with glume blotch severity in the field on all cultivars in some test locations, but not in others. However, the pathogenicity patterns expressed by the 14 isolates of S. nodorum were not correlated with geographic origin. Pathogenic interactions were classified as resistant, intermediate or susceptible. The magnitude of pathogenic interaction within the intermediate class was relatively low and since no isolate was found virulent on the uniformly resistant cultivars, no attempt was made to classify pathogenicity patterns into defined physiologic races.

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