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Relationship Between Yield Loss and Area Under the Wheat Stem Rust and Leaf Rust Progress Curves. G. W. Buchenau, Associate Professor, Plant Science Department, South Dakota State University, Brookings 57006; Phytopathology 65:1317-1318. DOI: 10.1094/Phyto-65-1317.

Whole-culm area under wheat stem rust and leaf rust curves (AUC) was determined by plotting rust as logits from +5 to –5 versus time for each of the top three leaves and the stem. The 40-day time interval was standardized for each organ; flag leaf–10 days before, to 30 days after heading; 2nd (penultimate) leaf–17 days before, to 23 days after heading; 3rd (antipenultimate) leaf–24 days before, to 16 days after heading; stem–heading to 40 days thereafter. Whole-culm AUC was defined as the sum of the top three-leaf average + stem areas under the curve, expressed in percent. Yield and percent yield loss were correlated with, and regressed respectively on, AUC in 13 fungicide tests covering an 8-year period. Correlation coefficients (r) varied from –0.69 to –0.99, were not significantly different among tests, and the estimate of a common r was –0.93. The null hypothesis that regression coefficients (b) = 1% loss of yield for each percent area under the curve was rejected in 2 of 13 tests.

Additional keywords: Puccinia graminis tritici, Puccinia recondita tritici, epidemiology.