VIEW ARTICLE

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.