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Sclerotinia Head Rot of Sunflower in North Dakota: 1986 Incidence, Effect on Yield and Oil Components, and Sources of Resistance. T. J. Gulya, USDA-ARS Research Pathologist, Northern Crop Science Lab, Box 5677, North Dakota State University, Fargo 58105. B. A. Vick, and B. D. Nelson. USDA-ARS Research Chemist, Northern Crop Science Lab, Box 5677, North Dakota State University, Fargo 58105, and Assistant Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis. 73:504-507. Accepted for publication 13 February 1989. 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, 1989. DOI: 10.1094/PD-73-0504.

Sclerotinia head rot of sunflower was observed in 98% of surveyed fields in eastern North Dakota in 1986. An estimated 10.2% of the crop was affected, which was a 200-fold increase over that recorded in 1984. The primary factor responsible for the epidemic was higher than normal precipitation during early August, which coincided with the blooming period. Yield loss, primarily due to reduction in seed number and seed weight and to disintegration of rotted heads, was estimated at 4.2%. Head rot caused a small but significant decrease in oil content and a significant increase in free fatty acid content. The proportions of palmitic, stearic, oleic, and linoleic acids were unaffected by head rot. Twenty-six of 164 genotypes tested, including open-pollinated varieties, wild Helianthus annuus accessions, and experimental hybrids, had significantly less head rot than the hybrid 894 check. Two genotypes, PI 377530 and PI 380571, exhibited significantly more resistance to both head rot and Sclerotinia wilt than the 894 check.