Figure 3.

Examples of infection types (ITs) on the disease rating scale as developed by Murphy (1935). ITs are used to score seedling resistance and to conduct physiological race assignments of Puccinia coronata f. sp. avenae. Incompatible reactions include the following: 0, no urediniospores; fleck (;), presence of flecks; 1, few small pustules; 2, small pustules, presence of green islands; all of these may be accompanied by necrosis (N) and/or chlorosis (C). Compatible reactions include the following: 3, large pustules surrounded by chlorotic halos; 4, large pustules, often coalescing. Those illustrated here (photographs by R. F. Park) were scored as, left to right: 0, ;–N, ;C, ;+C, ;1C, ;1N, 12C, 2N, 2, 3 and 4.