Effect of Placement of Inoculum of Gaeumannomyces graminis var. tritici on Severity of Take-all in Winter Wheat

Abstract

Take-all, caused by Gaeumannomyces graminis var. tritici, is one of the most important root diseases of wheat worldwide. Because of the lack of highly effective chemical control, cultural practices, such as crop rotation, play a major role in managing disease severity. In Kansas, many producers do not use these measures and continue to suffer losses from take-all. Greenhouse and field experiments were established to assess the effect of horizontal versus vertical distribution of G. graminis var. tritici inoculum on disease severity. Oat kernel inoculum was placed at 0 (seed level), 5, 10, or 15 cm below the wheat seed or 5, 10, or 15 cm to the side of the wheat seed at a depth of 5 cm. Inoculum spatial location and distance greatly influenced take-all. Experiments showed more severe losses due to take-all when inoculum was placed below the seed than to the side of the seed. Regression analyses were used to develop take-all risk models relating inoculum distance from the seed to yield loss. Quadratic models were a better fit for data from experiments where inoculum was placed to the side of the seed, whereas linear models significantly fit data from experiments where inoculum was positioned below the seed. Within the same direction, take-all decreased as the inoculum was placed at greater distances from the seed, often to insignificant levels at 10 to 15 cm. According to the regression models, significant reduction (≥50%) in take-all might be achieved by plowing under the infested residues (crowns) to depths greater than 15 cm, or placing seed >6.0 cm to the side of inoculum. Therefore, under no-till conditions, sowing parallel to and exactly between the previous years' stubble rows (inoculum) might help manage take-all. These possibilities need to be investigated under field conditions.