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Variation in Pathogenicity, Virulence, and Aggressiveness of Septoria nodorum in Florida. Elizabeth A. Allingham, Graduate research assistant, Department of Plant Pathology, University of Florida, Gainesville 32611, Present address of senior author: Statewide Air Pollution Research Center, University of California, Riverside 92521; L. F. Jackson, assistant professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 71:1080-1085. Accepted for publication 4 February 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1080.

Pathogenicity, virulence, and aggressiveness of 282 isolates of Septoria nodorum, causal agent of glume blotch of wheat, were determined on eight wheat cultivars of varying resistance. Cultivar reactions, measured as percentage necrosis of seedling leaves, were classified into 253 different resistant patterns. Ninety-five isolates were pathogenic to all eight cultivars; 85, to seven; 54, to six; 32, to five; 11, to four; four, to three; and one, to two cultivars. An isolate was considered pathogenic if it caused necrosis in a greenhouse test. Virulence of the isolates varied; maximum necrosis induced in the cultivars after 12 days ranged from 13 to 80%. Isolates from commercial fields were less variable in pathogenicity and more virulent than those from research plots. Aggressiveness, measured as the time to produce the first necrosis on seedling leaves of the cultivar Potomac, varied from three to 10 days after inoculation. Pathogenic and virulent types were present in differing frequencies and distributions in subpopulations defined in terms of geographic origin and year of isolation.

Additional keywords: Triticum aestivum L. em. Thell, host resistance.