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Reactions of Helianthus annuus and H. tuberosus Plant Introductions to Alternaria helianthi. P. E. Lipps, Associate Professor, Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. L. J. Herr, Professor, Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 70:831-835. Accepted for publication 21 March 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-831.

Of 497 Helianthus annuus plant introduction accessions evaluated during 3 yr of field tests, only eight had equal or significantly (P = 0.05) less leaf blight than a commercial H. annuus hybrid when inoculated with Alternaria helianthi. No differences were detected between the commercial hybrid and the eight H. annuus accessions when inoculated in the greenhouse with conidial concentrations of 150, 300, 3,000, or 20,000/ ml. Of 13 H. tuberosus accessions tested during 2 yr of field tests, all had significantly less leaf blight than the commercial H. annuus hybrid. In greenhouse tests, using 20,000 conidia per milliliter, all H. tuberosus accessions had significantly lower disease indices (0.82.4) than the H. annuus hybrid (5.0), which was killed. H. tuberosus accessions developed four distinct lesion types dissimilar to those produced on H. annuus. Results indicate that H. tuberosus may be a good source of resistance to A. helianthi.