The Influence of Rotation Crops on Take-All Decline Phenomenon

Abstract

An irrigated site at Lind, Washington [USA], was planted 7 yr consecutively to winter wheat [Triticum aestivum] divided into 3 replications of 5 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 [Gaeumannomyces graminis var. tritici] decline phenomenon. The 5 rotation crops included potatoes [Solanum tuberosum ''Kennebec''], oats [Avena sativa ''Cayuse''], alfalfa [Medicago sativa], beans (common beans [Phaseolus vulgaris ''Pink Kidney''] the 1st yr and soybeans [Glycine max] the 2nd and 3rd yr), and a mixture of intermediate wheatgrass [Agropyron intermedium] and smooth brome [Bromus inermis]. 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 quardrants (subplots) and treated as follows: only natural inoculum of the take-all pathogen, G. graminis var. tritici, with no treatment; fumigated (methyl bromide); fumigated then reinfested with inoculum of G. graminis var. tritici; and not fumigated, but inoculum of G. graminis var. tritici introduced. Take-all from natural inoculum 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. 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 groups 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.