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Three Components of Slow Leaf-Rusting at Different Growth Stages in Wheat. H. W. Ohm, Assistant Professor, Department of Agronomy, Purdue University, Lafayette, IN 47907; G. E. Shaner, Associate Professor, Department of Botany and Plant Pathology, Purdue University, Lafayette, IN 47907. Phytopathology 66:1356-1360. Accepted for publication 7 May 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1356.

Latent period, pustule size, and number of pustules per square centimeter of leaf area of two slow-rusting [Suwon 85 and Purdue 6028A2-9-6-1, (P6028)] and two fast-rusting (Monon and Suwon 92) cultivars were compared in greenhouse and field inoculations with Puccinia recondita f. sp. tritici. The appearance of pustules was protracted on Suwon 85 and P6028 compared to Suwon 92 and Monon. Thus, the latent period for Suwon 85 and P6028 was longer by a factor of 1.2 to 1.8 compared to that of Suwon 92 and Monon. Pustule size on the two slow-rusting cultivars was four- to six-tenths of that on the two fast-rusting cultivars. Pustule size was largest on the flag leaf compared to that on the first and second leaves below the flag leaf for all cultivars. Latent period was longest and pustule size was most restricted on plants of Suwon 85 and P6028 which were inoculated in the boot stage compared to when plants were inoculated at six other plant growth stages. Suwon 85 consistently developed fewer pustules per square centimeter of leaf area than Suwon 92, Monon, or P6028 in greenhouse experiments. Leaf rust severity was less and pustule size was smaller in the field for the two slow-rusting cultivars than for Suwon 92 and Monon.

Additional keywords: general resistance, horizontal resistance, nonspecific resistance, epidemiology.