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Resistant Winter Wheats Compared at Differing Growth Stages and Leaf Positions for Tan Spot Severity. D. J. Cox, Assistant Professor, Department of Agronomy, North Dakota State University, Fargo 58105. R. M. Hosford, Jr., Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis. 71:883-886. Accepted for publication 15 May 1987. 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, 1987. DOI: 10.1094/PD-71-0883.

Resistance to tan spot, caused by Pyrenophora tritici-repentis, was ranked among 14 winter wheat genotypes previously determined to have some resistance. Resistance was compared among greenhouse-grown adult plants, vernalized seedlings, and unvernalized seedlings using ratings of lesion size recorded from each of the top three leaves. Regardless of growth stage, the oldest leaf was most severely spotted and the youngest leaf was the least severely spotted. Severity of spotting was lowest and separation of genotypes for level of resistance was best on adult-plant flag leaves in the greenhouse. The correlation of tan spot severity for greenhouse-grown plants with adult field plants was significant for adult greenhouse plants (r = 0.86) and high for vernalized seedlings (r = 0.64) and unvernalized seedlings (r = 0.79).

Keyword(s): Drechslera tritici-repentis, Helminthosporium tritici-repentis, Pyrenophora trichostoma, yellow leaf spot.