Relationship between eyespot severity and yield loss in winter wheat

SUMMARY Between 500 and 1000 winter wheat plants were taken at random immediately before harvest from crops with naturally or artificially created attacks of eyespot (Pseudocercosporella herpotrichoides (Fron) Deighton) at eight sites in eastern England from 1975 to 1979. The individual shoots of each plant were placed in one of four categories: healthy, or slightly, moderately or severely infected with eyespot. Healthy shoots were sub-divided into those from plants with all shoots healthy and those from plants with at least one infected shoot. Ears were threshed individually and average dry weight of grain per ear, grain number per ear and 1000-grain dry weight were computed for each infection category and both healthy shoot categories. Slight eyespot had no effect on yield. Moderate eyespot reduced yield per ear, grain number per ear and 1000-grain weight by 10, 8 and 5 per cent respectively; severe eyespot caused corresponding losses of 36, 29 and 15 per cent. Healthy shoots showed no apparent compensation for yield loss in eyespot-infected shoots on the same plant. The equation y= O.lX1+ 0.36x2, where y= percentage yield loss, x1= percentage of moderately infected shoots and x2= percentage of severely infected shoots, was applied to the results of ADAS winter wheat disease surveys from 1975 to 1980. National yield losses due to eyespot in these years were estimated tobe 0.9, 0.3, 1.1, 1.2, 0.7 and 0.3 per cent respectively.

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