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Some Effects of Moderate Adult Resistance to Crown Rust of Oats. Allen S. Heagle, Former Research Assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55101, Present address of senior author: Crops Research Division, ARS, USDA, National Air Pollution Control Administration, North Carolina State University, Raleigh 27607; M. B. Moore, Associate Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55101. Phytopathology 60:461-466. Accepted for publication 9 October 1969. DOI: 10.1094/Phyto-60-461.

The oat (Avena sativa) varieties Portage, Ajax, Minhafer, Lodi, and Rodney were consistently moderately resistant to moderately susceptible to crown rust (Puccinia coronata f. sp. avenae) when grown adjacent to buckthorn (Rhamnus cathartica), whereas most other commercial oat varieties including Coachman, Bonkee, and Ortley were susceptible. In 3 years of tests, the spread of crown rust from inoculated centers was much less in plots of the moderately resistant varieties than in the susceptible varieties. In comparisons of rust development in adult plants there were fewer infections, hyphal growth was retarded, the number of days to onset of sporulation was greater, pustules were smaller, and fewer spores were produced per pustule in Portage than Coachman. This was so at low (10-15 C) and at moderate (21-26 C) temperatures with each of the two races used. The same relationship existed in seedling plants of the two varieties, but to a lesser degree. Present indications are that this moderate resistance is largely nonspecific, that it increases with the age of the plant, and that it may be of considerable value.