Use of the Modified Gregory Model to Describe Primary Disease Gradients of Wheat Leaf Rust Produced From Area Sources of Inoculum

Primary disease gradients of wheat (Triticum aestivum) leaf rust (induced by Puccinia recondita) were studied around 3.66- x 3.66-m sources of infection in two fields in both Pendleton and Corvallis, OR. The gradients were described well by the modified Gregory model, y = a(x' + c) -b , in which y is the number of infections per unit area, a is the number of infections per unit area at 1 - c units of distance from the source, x' is the distance from the center of the source to the center of a receptor of spores, c is a truncation factor that provides for a finite y-intercept when x' = 0, and b is a measure of the steepness of the gradient. (...)