Relationship between Yield Loss and Severity of Yellow Rust Recorded on a Large Number of Single Stems of Winter Wheat

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SUMMARYSingle stems of winter wheat cv. Maris Templar were selected at random along traverses of primary foci of yellow rust (Puccinia striiformis Westend) in a commercial crop. Severity of the disease was recorded as the percentage area affected on the flag and second leaves at the milky‐ripe growth stage. The ears were harvested when ripe and threshed individually. Grain weight per ear and mean weight of single grains were negatively correlated with disease severity, but there was no significant relationship with the number of grains per ear. The co‐efficient of linear regression of percentage loss on flag leaf rust severity were 0.41 and 0.39 for equations based on single grain weight and total yield per ear respectively. Transformation of percentage yellow rust by exponents of 1.2 and 1.35 led to co‐efficient of 0.18 and 0.09 respectively for the regression of percentage loss in single grain weight and yield per ear on disease level.I am indebted to Mrs. P. A. Waples, Miss N. Parsons and Messrs. R. W. Polley, J. G. Waples and J. D. S. Clarkson for their invaluable help in obtaining the data for this work.