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Growth of Uredinia of Puccinia recondita in Leaves of Slow- and Fast-Rusting Wheat Cultivars. Gregory Shaner, Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Phytopathology 73:931-935. Accepted for publication 14 January 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-931.

Rates of expansion of the surface areas of uredinia of Puccinia recondita in flag leaves of slow- and fast-rusting wheat cultivars (as judged by latent period and final uredinium size) were studied. Uredinia grew linearly with time and at a significantly faster rate in fast-rusting cultivars than in slow-rusting cultivars. Average rates for the fast-rusting cultivars Morocco, Monon, and Suwon 92 were 0.07, 0.05, and 0.04 mm2/day, respectively. Average rates for the slow-rusting cultivars CI 13227 and Suwon 85 were 0.03 and 0.02 mm2/day, respectively. Uredinia reached maximum size 8- 10 days after first becoming visible. The more densely uredinia were packed on a leaf, the slower they grew. Simulations of leaf rust epidemics suggested that a slow growth rate of uredinia would be a significant factor in retarding disease development in the field.

Additional keywords: durable resistance, general resistance, pustule growth, SLORUS, Triticum aestivum.