Scoring stem rust

Detailed outlines for recording stem rust intensities in cereals are based upon:

  • Severity (percentage of rust infection on the plant) and
  • Field response (type of disease reaction).

Severity is recorded as a percentage, according to the modifed Cobb scale. This recording process relies upon visual observations, and it is common to use the following intervals: Trace / 5 / 10 / 20 / 40 / 60 / 100 percent infection.

Field response is recorded using the following letters:

O No visible infection on plant.
R Resistant: visible chlorosis or necrosis, no uredia are present.
MR Moderately Resistant: small uredia are present and surrounded by either chlorotic or necrotic areas.
M Intermediate: variable sized uredia are present; some with chlorosis, necrosis, or both.
MS Moderately Susceptible: medium sized uredia are present and possible surrounded by chlorotic areas.
S Susceptible: Large uredia are present, generally with little or no chlorosis and no necrosis.

Severity and field response readings are usually combined.
For example:

tR = Trace severity with a resistant field response.
5MR = 5% severity with a moderately resistant field response.
60S = 60% severity with a susceptible field response.

Figure 1. Examples of scoring Stem rust severity

Figure 2. Examples of scoring Stem rust field responses

RMRMSS