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Individual and Cumulative Effects of Long Latent Period and Low Infection Type Reactions to Puccinia recondita in Triticale. Jeffrey Wilson, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, Present address: USDA-ARS, Coastal Plain Experiment Station, Tifton, GA 31793-0748; Gregory Shaner, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 79:101-108. Accepted for publication 1 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-101.

Triticale PI 429155 was selected as a possible source of leaf-rust resistance for wheat. This cultivar expresses an infection type (IT) 1* and a latent period (T50) of about 14 days when inoculated with culture 7434-1-IT of Puccinia recondita. The effects of the incomplete hypersensitivity and slow-rusting resistance of PI 429155 were evaluated by separating the genetic factors for resistant IT and long T50 into different experimental cultivars, measuring the components of resistance on adult plants, and evaluating the resistances in epidemics. The derived cultivars possessed either no resistance factors (susceptible, SUSC), the factors for long T50 and susceptible IT (slow rusting, SR), the factors for resistant IT and moderately short T50 (hypersensitive resistance, HR), or factors for both forms of resistance combined (slow-rusting and hypersensitive resistances, SR + HR). SR, HR, and SR + HR all reduced the infection frequency on flag leaves. The IT, T50, and uredinium areas of SUSC, SR, HR, and SR + HR were IT 4, 3, 2, and 1*; 7.1, 13.0, 9.5, and 14.3 days; and 0.282, 0.124, 0.093, and 0.069 mm2, respectively. The gamma distribution fit the pattern of spores produced per uredinium per day, measured from 7 to 30 days after inoculation. Cumulative spores produced per uredinium on SR, HR, and SR + HR were 27.5, 16.4, and 13.6% of that produced on SUSC. The long T50 of SR provided greater disease control than the reduced sporulation and smaller uredinia of HR in computer-generated models of rust epidemics and in hill plots in the field in 1986 and 1987.