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Reaction of Winter Oat Germ Plasm to an Epidemic of Oat Powdery Mildew. S. Leath, USDA-ARS, North Carolina State University, Raleigh 27695-7616. P. L. Bruckner, and J. P. Wilson. University of Georgia, Tifton 31793-0748, and USDA-ARS, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748. Plant Dis. 75:807-809. Accepted for publication 28 January 1991. 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, 1991. DOI: 10.1094/PD-75-0807.

In the spring of 1989, an epidemic of oat powdery mildew occurred naturally in four randomized blocks near Tifton, Georgia, in which 31 winter oat lines had been planted in the fall of 1988. Plots were rated on 14 and 18 April for percentage of foliage covered with mildew and for infection type (04 scale). Differences existed among cultivars on both assessment dates. Severity levels increased from a mean of 29.2 to 32.9% between assessment dates, and all cultivars showed symptoms; oat lines ranged from 7.5 to 59.4% in severity and from 1.4 to 4.0 in infection type. The same cultivars were tested in a growth chamber with a pure culture of Blumeria graminis f. sp. avenae recovered from oat cultivar Brooks to determine if they could be effectively screened as seedlings under controlled conditions. Seedling reaction means ranged from 2.3 to 7.0 on a 09 scale of powdery mildew severity and from 1.8 to 3.8 on a 04 scale for infection type. Severity and infection type data were correlated in both field (r = 0.84, P < 0.01) and controlled environments (r = 0.500.67, P < 0.01). Severities in the field and growth chamber also were correlated (r = 0.370.46, P < 0.05). Based on all data, the most resistant lines were AR-111-2, AR-02848, AR-820B-669, and GA-T81-1251. The lines PA 8014-608, PA 7915-1342, and TAMO 386 were the most susceptible. Several lines that may express adult plant resistance showed large differences between field and greenhouse evaluations; NK Coker 86-10, NK Coker 716, and Simpson showed high levels of resistance only in the field. This may be due to the existence of a mixture of pathogen phenotypes in the Southeast, despite the fact that no cleistothecia were observed in North Carolina or Georgia, making evaluation with a single isolate undesirable.