VIEW ARTICLE

Ecology and Epidemiology

Effects of Wheat Chaff and Tillage on Inoculum Density of Pythium ultimum in the Pacific Northwest. C. M. Rush, Agricultural Research Service, U.S. Department of Agriculture, Irrigated Agriculture Research and Extension Center, P.O. Box 30, Prosser, WA 99350, Present address: Texas Agric. Exp. Station, 6500 Amarillo Blvd. West, Amarillo, TX 79106; R. E. Ramig(2), and J. M. Kraft(3). (2)(3)Agricultural Research Service, U.S. Department of Agriculture, Irrigated Agriculture Research and Extension Center, P.O. Box 30, Prosser, WA 99350. Phytopathology 76:1330-1332. Accepted for publication 24 June 1986. 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, 1986. DOI: 10.1094/Phyto-76-1330.

Studies were conducted to evaluate the effects of wheat chaff and tillage on inoculum density of Pythium ultimum in the field, and to determine the availability of chaff as a food source for P. ultimum. Soil and chaff samples were taken from two field sites five times between the 1984 wheat and 1985 pea harvest. Inoculum density was not affected by sampling time, tillage, or amount of chaff in the two field soils. In laboratory studies, when wheat chaff was collected from the field 1 wk after harvest and added to soil infested with P. ultimum in the laboratory, it became 90% colonized. Chaff collected 3 wk later became only 10% colonized. Except at the first collection date, autoclaving the chaff significantly increased colonization. Wheat chaff was not colonized by P. ultimum in the field and chaff from the field quickly became unavailable as a food source for P. ultimum even under optimum moisture and temperature conditions for saprophytic development. Lack of colonization of wheat chaff by P. ultimum in the field is likely due to unfavorable environmental conditions at harvest for saprophytic development and previous colonization by other microorganisms.