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Survival of Puccinia recondita and P. graminis Urediniospores as Affected by Exposure to Weather Conditions at One Meter. M. G. Eversmeyer, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture and Department of Plant Pathology, Kansas State University, Manhattan 66506-5502; C. L. Kramer, professor, Division of Biology, Kansas State University, Manhattan 66506-5502. Phytopathology 84:332-335. Accepted for publication 3 January 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/Phyto-84-332.

Viable urediniospores and dormant mycelia are the principal inoculum sources that contribute to the establishment and development of destructive wheat rust epidemics in the central Great Plains of the United States. Inoculum survival was measured by exposing urediniospores of Puccinia recondita and P. graminis to field conditions occurring at 1 m above ground level throughout two crop years. Four phases (summer, fall, winter, and spring) important in survival of urediniospores as potential inoculum in epidemic development were used in data analysis. Survival of P. recondita and P. graminis urediniospores during wheat dormancy (winter) was reduced to 1011 and 1721%, respectively, within 24 h. Only 2% of P. recondita and 3% of P. graminis urediniospores survived 72 h of subfreezing temperatures, and no spores germinated after 96 h. Survival of inoculum exposed in the field during wheat green-up (spring), with daily temperatures of 18 to 4 C, was measured at 1020% after 120 h. Trace amounts of P. recondita urediniospores remained viable for 336 h and less than 1% of P. graminis urediniospores survived for up to 456 h. During the harvest period (summer), when maximum temperatures were above 30 C and minimum temperatures were above 10 C, at least 60% of urediniospores of both species survived for 120 h, and trace amounts of germination were observed for up to 456 h. During the period of wheat-stand establishment (fall), over 50% of the urediniospores exposed in the field remained viable for 120 h, with trace amounts of survival for 456 h. Survival of urediniospores exposed to below 0 C at 1 m above ground level was not significantly different at 2,300 versus 335 m above sea level. No significant differences (P = 0.05) in survival occurred among isolates of either P. recondita or P. graminis when exposed to extended subfreezing temperatures during wheat dormancy. However, differences among isolates were observed at 72 h with extended exposure to temperatures above 0 C.

Additional keywords: dispersal, primary inoculum, Triticum aestivum, urediniospore germination.