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Resistance

Response of Susceptible and Slow Leaf-Rusting Wheats to Infection by Puccinia recondita. Gregory Shaner, Associate Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Herbert W. Ohm(2), and Robert E. Finney(3). (2)(3)Associate Professor, Department of Agronomy, and Research Associate, respectively, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 68:471-475. Accepted for publication 24 August 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-471.

Flag leaves of slow leaf-rusting winter wheat cultivars Suwon 85 and P6028 and susceptible cultivars Monon and Suwon 92 were inoculated uniformly with urediospores of Puccinia recondita in the greenhouse to measure components of slow-rusting resistance. Uredia first appeared on Monon and Suwon 92 on day 6 after inoculation and all uredia had appeared by day 9 or 10. Uredia first appeared on Suwon 85 and P6028 on day 7 but all uredia did not appear until day 12 or 13. Throughout most of the period of opening of uredia, development lagged 2-4 days on Suwon 85 and P6028. The final numbers of uredia per square centimeter on Suwon 85 and P6028 were less than on Monon and Suwon 92, but the difference was not statistically significant. For all cultivars, approximately 12% of the spores applied to the leaf gave rise to uredia. Uredium size was inversely related to the density of uredia, but uredia were consistently larger on Monon and Suwon 92 than on Suwon 85 and P6028. The production of more urediospores per day per uredium on Monon and Suwon 92, compared to Suwon 85, was the result of larger uredia on these two cultivars. Low production of urediospores on P6028 was due to less production per square millimeter of uredium and to smaller uredia. The effects of the resistance mechanisms in Suwon 85 and P6028 would be cumulative over the several infection cycles that occur during epidemic development in the field and should result in a much lower leaf rust severity on them compared to susceptible cultivars.

Additional keywords: general resistance, horizontal resistance, nonspecific resistance, epidemiology, Triticum aestivum, breeding for resistance.