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Receptivity, Incubation Period, and Lesion Size as Criteria for Screening Barley Genotypes for Resistance to Pyrenophora teres. Forrest Weston Nutter, Jr.,, Former graduate research assistant, Department of Plant Pathology, North Dakota State University, Fargo 58105, Present address of senior author: assistant professor, Department of Plant Pathology, University of Georgia, Athens 30602; Vernyl D. Pederson, professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Phytopathology 75:603-606. Accepted for publication 28 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-603.

Barley genotypes that limited the size of lesions caused by Pyrenophora teres did not always reduce receptivity (number of lesions per unit leaf area). Receptivity on five barley genotypes increased as the duration of leaf wetness (hours) was increased following inoculation of seedlings with spores of P. teres. The linear model Y = β0 + β1 X + E adequately described the relationship between the duration of leaf wetness (X) and increase in receptivity (Y) on five barley genotypes. Either the rate parameter (β1) or relative receptivity (tested for a 15-hr leaf wetness duration period) could be used to quantify resistance that reduces receptivity. Cultivar Glenn had the highest receptivity and breeding line ND B112 the lowest. Lesion size was not greatly affected by increasing leaf wetness duration up to 24 hr, but lesion size had nearly doubled after 40 hr. Differences in incubation period were detected by determining the time (hours) within which 50% of the lesions appeared on each barley genotype. ND B112 had the greatest effect on delaying the appearance of lesions. These experiments suggest that plant breeders could increase the level of resistance to P. teres by utilizing barley genotypes that restrict lesion size and reduce receptivity and by making appropriate crosses and selections to combine these resistance components.