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Genetic Analysis of Changes in Scald Resistance in Barley Composite Cross V. L. F. Jackson, Extension agronomist, Department of Agronomy, University of California, Davis 95616; R. K. Webster(2), R. W. Allard(3), and A. L. Kahler(4). (2)Professor, Department of Plant Pathology, University of California, Davis 95616; (3)Professor, Department of Genetics and Department of Agronomy, University of California, Davis 95616; (4)Plant geneticist, USDA, ARS, and associate professor of Plant Sciences, Northern Grain Insects Research Laboratory, RR #3, Brookings, South Dakota State University, Brookings 57007. Phytopathology 72:1069-1072. Accepted for publication 5 February 1982. 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, 1982.. DOI: 10.1094/Phyto-72-1069.

Families derived by self-pollinating a random sample of plants from four generations (F5, F12, F23, and F32) of barley Composite Cross V were inoculated with isolates of races 40, 61, 72, 74 of Rhynchosporium secalis and scored as resistant, susceptible or segregating for scald disease reaction. This population, which was synthesized from intercrosses among 30 barley cultivars, has been grown annually at Davis, CA, under standard agricultural conditions without conscious selection. Many different family types were found in all generations, including numerous segregating families. A test for randomness showed that families susceptible to all four races and families resistant to three races were more frequent than expected under the assumption that resistance to different races is independent. Positive correlations were found between resistance to races 40, 61, and 74, but resistance to race 72 was independent of resistance to the other races. Possible reasons for these correlations are discussed. The appearance, disappearance, and reappearance of different family types in successive generations and the changes in frequency of multiply resistant families appear to represent responses to biological stress caused by the variable and shifting pathogen population.

Additional keywords: conservation of resistance, inheritance of resistance, plant breeding.