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Relationship Between Leaf Roll Symptoms and Yield in Netted Gem Potato. F. R. Harper, Plant Pathologist, Research Station, Agriculture Canada, Lethbridge, Alberta, Canada T1J 4B1; G. A. Nelson(2), and U. J. Pittman(3). (2)(3)Plant Pathologist and Agronomist, Research Station, Agriculture Canada, Lethbridge, Alberta, Canada T1J 4B1. Phytopathology 65:1242-1244. Accepted for publication 2 June 1975. DOI: 10.1094/Phyto-65-1242.

The relationship between symptom severity and yield of tubers was determined in field experiments with Netted Gem potatoes. Plants with slight, moderate, and severe symptoms yielded 65, 80, and 92% less than those with no symptoms. Plants with mild symptoms (slight rolling of the leaves, but no stunting or chlorosis) yielded as much as those with no symptoms. The equation: Yield loss (%) = 100 (n_dk)/(n_h + n_d) where n_d is the number of plants with slight, moderate, or severe symptoms; n_h is the number with no or mild symptoms; and k = 0.8, accurately estimated the loss in yield in both 1970 and 1972 field plot tests. A second equation, containing three constants, is given for use where greater accuracy is required.