Influence of crop rotation on common root rot of wheat and barley

Three-year crop rotations involving combinations of wheat, barley and flax were compared for their effect on common root rot [Cochliobolus sativus] in subsequent crops of wheat and barley at sites with different cropping histories. Rotations that ended with two or more years of flax reduced the severity of common root rot in both of the cereal crops and decreased the amount of viable inoculum of C. sativus in the soil. In wheat and barley, common root rot severity was lower after rotations in which the other cereal had been grown for the final 2 years than after continuous cultivation of the same crop. Severity in barley increased when longterm cropping of wheat, flax or oats was followed by 2 years of barley. At sites where common root rot was severe in barley, 2 years of wheat production usually increased severity in wheat. The virulence of C. sativus appeared to be selectively enhanced or depressed by the host crops in the rotations. Significant differences in common root rot severity in resistant and susceptible lines or cultivars of the same crop were usually observed in all rotations. The effect of rotation on the yield of the subsequent wheat or barley crop was inconsistent and not always related to differences in severity. The root rot resistant barley cultivar Bonanza out-yielded the susceptible cultivar Gateway at sites where common root rot was generally severe in barley.