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The Influence of Rotation Crops on Take-All Decline Phenomenon. R. James Cook, Research plant pathologist, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Washington State University, Pullman 99164; Phytopathology 71:189-192 . Accepted for publication 15 July 1980. 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, 1981. DOI: 10.1094/Phyto-71-189.

An irrigated site at Lind, WA, was planted 7 yr consecutively to winter wheat, divided into three replications of five rotation (break) crops for 3 yr, and finally in the 11th yr all to wheat again, to determine the influence of rotation crops on the take-all decline phenomenon. The five rotation crops included potatoes, oats, alfalfa, beans (common beans the first yr and soy-beans the second and third yr), and a mixture of intermediate wheat grass and smooth brome. A given crop was in the same main plot each of the 3 yr. Spring wheat was grown in a main plot in each replicate each year as a control. Before the entire experimental area was planted to wheat in the 11th yr, each main plot was divided further into quadrants (subplots) and treated as follows: (i) only natural inoculum of the take-all pathogen, Gaeumannomyces graminis var. tritici, with no treatment; (ii) fumigated (methyl bromide); (iii) fumigated then reinfested with inoculum of G. graminis var. tritici; and (iv) not fumigated, but inoculum of G. graminis var. tritici introduced. Take-all from natural inoculum (i above) was common on wheat plants in the 11th yr in plots previously planted to wheat, the grass mixture, or soybeans, but was mild or nonexistent on wheat after oats, potatoes, or alfalfa. When inoculum of G. graminis was introduced, take-all was severe in plots previously planted to potatoes, oats, alfalfa, or beans, whether or not the soil had been fumigated (treatments iii and iv above). In contrast, soil in plots previously planted to wheat or the grass mixture had to be fumigated before disease of such severity could develop in response to introduced inoculum of the pathogen. Soils cropped continuously to wheat or wheat in rotation with the grass mixture were suppressive to take-all; the other crops resulted in soil becoming highly conducive to take-all. Rotating with beans not only made the soil conducive to take-all, this crop apparently maintained a source of inoculum of the pathogen as well.

Additional keywords: biological control.