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Resistance in Winter Wheats to Geographically Differing Isolates of Pyrenophora tritici-repentis and Observations on Pseudoperithecia. M. Diaz de Ackermann, Plant Pathologist, Estacion Experimental, La Estanzuela, Colonia, Uruguay. R. M. Hosford, Jr., D. J. Cox, and J. J. Hammond. Professor, Department of Plant Pathology, Assistant Professor, and Professor, Department of Agronomy, North Dakota State University, Fargo 58105. Plant Dis. 72:1028-1031. Accepted for publication 30 June 1988. 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, 1988. DOI: 10.1094/PD-72-1028.

The winter wheats (Triticum aestivum) Carifen 12 and Red Chief were resistant, Roughrider was moderately resistant, and Brule and ND8001 were moderately susceptible, and the hard red spring wheat ND495 was susceptible, to nine virulent isolates (causing large tan spots on many genotypes) of the fungus Pyrenophora tritici-repentis from several areas of the Great Plains of North America. Lesion length separated these wheats for resistance. Isolates PTL1, PYD7, PYR72, Pti2, 1231CDA, 78-64, W38, 78-62, and Embden were highly virulent on the susceptible genotype, moderately to highly virulent on the moderately susceptible genotypes, and of low virulence on the moderately resistant to resistant genotypes. Isolates PT4, PTF3, and Buffalo were of low virulence (causing small tan spots) or avirulent (causing tiny dark flecks) on all genotypes. Isolate genotype specificity was not evident. Most fungal isolates retained their vigor and virulence after 4 yr in liquid nitrogen. On corn leaves, the fungal pseudoperithecia developed unusually long necks.

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