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Effect of Flooding and Temperature on Incidence and Severity of Safflower Seedling Rust and Viability of Puccinia carthami Teliospores. J. M. Klisiewicz, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis, CA 95616; Phytopathology 67:787-790. Accepted for publication 13 December 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-787.

Soil infested with Puccinia carthami was flooded under different time-temperature regimes in controlled-environment chambers. The incidence and severity of rust on safflower seedlings decreased in soils following flooding under increasing temperature and time. Rust was completely controlled in soil flooded for 4 and 7 days at temperatures maintained at a constant 36 or 39 C. Flooding at day-night temperature regimes varying from 36 to 26 C and 39 to 29 C for 4 and 7 days controlled rust in all but the 36-26 C, 4-day regime. Incidence and severity of rust were markedly reduced after soil was flooded for 7 days at 30 and 33 C and progressively decreased with prolonged flooding at 12, 18, and 24 C. Disease incidence in the field was significantly lower with flooding than without. Viability of teliospores was reduced when they were submersed in water or dispersed on agar at 18 to 39 C for 2-14 days. Spores were not viable after a minimum treatment of 4 days in water or on agar at 36 and 39 C. Loss of viability was slower as exposure temperature decreased. When spore suspensions in water at 30 and 33 C for 4 days were aerated, a small increase in germination occurred in subsequent assays.