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Environmental Effects on Inoculum Quality of Dormant Rust Uredospores. M. V. Wiese, Department of Botany and Plant Pathology, Michigan State University, E. Lansing, 48824, Current address of senior author: Department of Plant and Soil Sciences, University of Idaho, Moscow, 83843; A. V. Ravenscroft, Department of Botany and Plant Pathology, Michigan State University, E. Lansing, 48824. Phytopathology 69:1106-1108. Accepted for publication 12 April 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1106.

Uredospores of Puccinia graminis f. sp. tritici and P. recondita f. sp. tritici, fungi which cause stem rust and leaf rust of wheat, respectively, were produced in the greenhouse on wheat seedlings (Triticum aestivum ‘Little Club’). Newly harvested, mature, dormant uredospores immediately were subjected to specific light, temperature, and relative humidity (RH) treatments for 24 and 48 hr, then tested for germinability and infectivity. Compared with untreated spores, which consistently germinated >91% and which produced 60 ± 20 infections per leaf in standardized tests, germination and infectivity were reduced or eliminated by increased treatment temperatures, especially above 25 C. Germinability and especially infectivity further were reduced by exposure to 100% RH. Supplemental light reduced or eliminated the detrimental effects of high RH, but otherwise caused no measurable effect. Reductions in infections per leaf and in infection efficiency always were proportionally greater than were losses in germinability. The possible epidemiological significance of these findings is discussed.

Additional keywords: spore germination, epidemiology.