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Moisture Effects on the Discharge and Survival of Conidia of Septoria tritici. F. J. Gough, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, Oklahoma State University, Stillwater 74076, Present address: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; T. S. Lee, U.S. Department of Plant Pathology, Oklahoma State University. Phytopathology 75:180-182. Accepted for publication 4 September 1984. 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, 1985. DOI: 10.1094/Phyto-75-180.

The effect of relative humidity (RH) on the discharge of conidia of Septoria tritici and their longevity in cirri was tested by suspending pycnidia in leaf lesions above water and solutions of NaCl and NaOH in sealed test tubes held at 25 0.2 C in a water bath. Pycnidia held for 48 hr at about 100% RH discharged twice as many conidia as those held at 98%, and 11 to 23 times as many as those held at 86%. Conidia in cirri on top of pycnidia remained 100% viable for 15 days in atmospheres of 35, 45, 55, 65, 75, and 85% RH. But between the 15th and 20th day viability of conidia held at 65% and above dropped to 5- 10%, then declined to less than 2% by the 30th day, and to 0 by the 50th day. At 55% RH, 60% of the conidia were viable, and at 45 and 35% RH, 80% were viable after 60 days. Conidia within pycnidia held at 35% RH were 100% viable after 132 days.

Additional keywords: conidia, epidemiology, germination, speckled leaf blotch, Triticum aestivum, water potential.