Characterization of leaf rust progress in wheat cultivars with different resistance levels and sowing dates

A better understanding of leaf rust progress curves is highly desired by wheat breeders and pathologists to achieve more precise and ambitious predictors of disease development. High variations in leaf rust progress across different wheat cropping systems can cause difficulties and uncertainties for study of disease increase rate. A number of standard curves were fitted to a four-season data set on leaf rust severity ratings to find further descriptive disease curve elements for wheat cultivars under different sowing dates. A Gaussian model provided the best fitted parameters to be considered as wheat leaf rust progress curve elements. According to H-test results, sowing date and cultivar resistance factors significantly affected the area under disease progress curve (AUDPC), maximum disease severity, and Gaussian parameters m and s. Multivariate analysis indicated considerable association among AUDPC, leaf rust onset, maximum disease severity, and three Gaussian parameters. With this new proposed approach, a better understanding of the variables to be measured for estimating wheat leaf rust development will be obtained.