Assessment of tolerance in wheat and barley to common root rot (Cochliobolus sativus)

Field tests at Saskatoon, Saskatchewan, Canada indicated no evidence of tolerance to common root rot in four spring wheat cultivars. There was a relationship between increased yield losses and increasing disease. In barley, the relationship was inconsistent in four cultivars and there was evidence of tolerance or recovery in Melvin with the number of seeds per head increasing with the level of disease. In Queensland, Australia there was evidence of tolerance in the wheat cultivar Banks across two locations, but the response was not consistent in all cultivars. Dry matter loss at immature growth stages was not related to grain yield loss. The inconsistent expression of tolerance in wheat, the difficulty of assessing it, and the difficulty of distinguishing tolerance from recovery suggest that the assessment of tolerance is not a reliable method of determining the reaction to common root rot. The relationship between loss in dry matter and grain yield, as disease increased, indicates that disease assessment should continue to be based on severity of symptoms. The evidence of tolerance to common root rot in barley suggests research on tolerance should concentrate on barley instead of wheat. Key words: Cochliobolus sativus, common root rot, tolerance, wheat, barley