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Quantitative Resistance to Pyrenophora teres f. teres in Barley. Brian J. Steffenson, Former graduate research assistant, Department of Plant Pathology, University of California, Davis 95616, Present address: Department of Plant Pathology, North Dakota State University, P.O. Box 5012, Fargo 58105; R. K. Webster, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 82:407-411. Accepted for publication 21 November 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-407.

Resistance to the net blotch pathogen Pyrenophora teres f. teres was studied in seven barley genotypes using four criteria: 1) infection response (size and type of lesion), 2) area under the disease progress curve (AUDPC), 3) terminal severity (TS), and 4) apparent infection rate (r). The susceptible check, Kombar, and resistant check, Tifang, differed greatly in reaction to P. t. f. teres in the field during the 2-yr study; Kombar exhibited high or compatible (susceptible to moderately susceptible) infection responses and high TS and AUDPC values, whereas Tifang exhibited low or incompatible (resistant) infection responses and low TS and AUDPC values. Atlas, Beecher, Hazera, Cape, and UC 603 displayed infection responses that indicated a degree of compatibility, but disease progress on each was significantly lower than that on Kombar as measured by AUDPC. Thus, these five genotypes possess different levels of quantitative resistance to P. t. f. teres. The environment and amount of inoculum may alter the expression of quantitative resistance since high net blotch severities were observed on the five genotypes during a severe epidemic in 198586 and low severities were observed during a moderate epidemic in 198687. Cape and UC 603 consistently exhibited the highest level of quantitative resistance as given by AUDPC and could serve as parents in programs breeding for this type of resistance in barley.