Slow leaf rust development on durum wheat

Several durum wheat (Triticitm durum) cultivars exhibiting susceptible or moderately susceptible reactions to the leaf rust fungus (Puccinia recondita tritici) were evaluated for slow rusting. Percentage severity and reactions for P. recondita tritici on each cultivar were evaluated periodically after initial infection. Logit analysis of disease progress curves was used to compare cultivars. The durum wheats consistently exhibited low rust severities in the field. The durums were always characterized by lower infection rates than the susceptible bread wheat cultivar Thatcher (Triticum aestivum). The area under the disease progress curve was smaller for the durum wheats than for Thatcher. The high correlation between apparent infection rate and the final rust severity indicated that final rust severity could be used as an indication of infection rate. The high correlation coefficient for the apparent infection rate between the two top leaves indicated that either leaf would provide an accurate evaluation of the cultivar. Yields of the durum wheat cultivars were not increased by controlling leaf rust. Yields of the susceptible bread wheat cultivar Thatcher were significantly increased by controlling leaf rust. The slow rusting displayed by the durum wheat cultivars studied apparently provide adequate protection against leaf rust under North Dakota conditions.