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Probits for Analyzing Latent Period Data in Studies of Slow Rusting Resistance. Gregory Shaner, Associate professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Phytopathology 70:1179-1182. Accepted for publication 3 June 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1179.

Probit analysis was applied to latent period data of wheat leaf rust. Analysis of data from monocyclic infection experiments in the greenhouse revealed a linear relationship between probit percent of uredinia erupted and days after infection. Coefficients of determination from linear regression analysis were greater than 0.91 for 32 of 33 sets of data analyzed. T₅₀, the day by which 50% of the uredinia have erupted, was calculated from the linear regression coefficient and y-intercept. T₅₀, which is analogous to the LD₅₀ of toxicology, characterizes the latent period of the disease and can be used to compare host genotypes for degree of slow rusting resistance. Latent period curves (percent uredinia erupted vs days after infection) generated from probit analysis statistics were quite similar to the original curves. The advantage of using T₅₀ over calculating a weighted latent period or directly estimating the day on which 50% of uredinia erupt, is that plants need not be inspected each day for percent uredinia erupted in order to calculate T₅₀. Alternate day inspections are sufficient and greatly reduce the time and effort associated with studying slow rusting or using it in a breeding program.