Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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research, as two new categories were added (Table 1).
Coefficient of Infection was calculated by multiplying the response value
with the intensity of infection in percent. Average Coefficient of Infection
(ACI) was derived from the sum of CI values of each entry divided by the
number of locations.
After some modifications, a rating scale for disease resistance was adopted
by PARC in 1982 for use with cereal rusts (Aslam, 1982), based on the scale by
Doling (1965) for selecting wheat varieties resistant to powdery mildew and
later adopted for farmers by the UK Agricultural Research Council (ARC).
The highest ACI of a candidate line is set at 100 and all other lines are
adjusted accordingly. This gives the Country Average Relative Percentage
Attack (CARPA). The 0–9 scale previously designated as Resistance Index (RI)
has been re-designated as RRI (Relative Resistance Index). From CARPA, RRI
is calculated on a 0 to 9 scale, where 0 denote most susceptible and 9 highly
resistant.
The RRI is calculated according to the following formula:
RRI = [(100 -CARPA) × 9] / 100
To illustrate the formula a hypothetical example is given in Table 2.
Table 2. Relative Resistance Index (RRI) calculated for three hypothetical samples
Location
variety
1 2 3 CI total ACI CARPA RRI
A 30S 10MR-MS 5S
CI 30.0 6.0 5.0 41.0 13.7 100 0
B Tr-R 30MR-MS 10MR
CI 0.2 18.0 4.0 22.2 7.4 54 4
C 5MS-S 10R-MR 5MR
CI 4.5 3.0 2.0 9.5 3.2 23.3 7
The desirable index and acceptable index numbers for rusts are:
• For yellow rust, desirable index is 7 and above, but 5 is acceptable.
• For leaf rust, desirable index is 7 and above, but 5 is acceptable.
Lines which, through yield testing, show a high degree of yield stability
even under high infection conditions, have their Index rating increased by +1.
Results and discussion
Final observations of yellow rust were recorded after full establishment of rust
and at physiological maturity of the international susceptible check and