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Evaluation of Oat Crown Rust Disease Parameters and Yield in Moderately Resistant Cultivars. L. L. Singleton, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Present address: Department of Plant Pathology, Oklahoma State University, Stillwater 74078; M. B. Moore(2), R. D. Wilcoxson(3) and M. F. Kernkamp(4). (2)(3)(4)Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 72:538-540. Accepted for publication 17 August 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-538.

Twelve oat cultivars that differed in susceptibility to crown rust caused by Puccinia coronata f. sp. avenae were evaluated during severe, moderate, and light epidemics in 1971 and 1972 at St. Paul and Rosemount, MN. A multiline (ML) cultivar and cultivars with the following crown rust reactions were evaluated: S = susceptible, M = moderate, ET = early telia, SR = slow ruster, and HR = highly resistant. The differences in both disease and yield parameters between the moderately resistant types (M, ML, ET, and SR) and the R and S cultivars were more distinct with increased epidemic severity. Correlations between disease severity and the ratios of yield or kernel weight in rusted and nonrusted subplots were negative and highly significant. Thus, crown rust reduced yields in direct proportion to disease severity; however, the yields of some moderately resistant types (66B1269, Minhafer, Iowa M70, and Portage) equaled or exceeded the yield of the HR types under severe epidemic conditions, even though rust development on them was greater.

Additional keywords: Avena sativa, race diversity, nonspecific resistance.