Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Experimental yield loss estimate
The yield component most affected by yellow rust was the kernel weight. A
loss of 41% was recorded in the experiment.
Overall yield loss estimate
The area planted to the susceptible
cv. Achtar was about 45% of the total
bread wheat area. The potential
average yield of the surveyed fields
was estimated to be 3.5 t/ha. The
estimated mean loss was 0.5 t/ha.
Thus, total yield loss on cv. Achtar is
estimated to be 100 000 tonne, worth
ca US$ 30 million. (Table 3)
Race identification
The isolates of yellow rust collected
from Morocco were of the same race.
They were identical to the race pattern of the aggressive strain spreading in
east Africa (Ethiopia/Eritrea) and West and Central Asia, i.e. virulence for Yr2,
Yr6, Yr7, Yr8, Yr9, Yr27 and YrSD.
Meteorological data analysis
Table 3. Estimated yield loss of bread
wheat due to yellow rust in the Sais region
and the Middle Atlas mountains
Area planted to bread wheat
Area planted to susceptible cv.
Achtar
Potential average yield (surveyed
fields)
Estimated mean loss (surveyed
fields)
Total production of cv. Achtar
Predicted production loss of cv.
Achtar
Monetary loss
280 000 ha
196 000 ha
3.5 t/ha
0.5 t/ha
700 000 t
100 000 t
US$ 30 million
The season 200/09 was in general cooler than the 30-year long-term average
for most of the months, starting from October, as shown for the two locations
of Rabat and Meknes (Tables 4a and 4b). The rainfall in this season was
abundant, early and regular. The amount of rainfall was about 30% more than
an average year (Tables 5a and 5b). Climatic conditions were therefore
favourable for yellow rust onset and its epidemic spread. We note that yellow
rust was becoming more prevalent in Morocco in the last few years. Thus, the
carry over of inoculum has become important, increasing the chances of the
pathogen surviving the summer. The prevailing summer weather conditions
were reported to have a profound influence on the yellow rust epidemic in the
following winter, spring and summer (Rapilly, 1979). If mean air temperatures
are above 30°C for long periods, the urediniospores and the fungus in the
lesions are inactivated. Thus, little inoculum carries over into the autumnwinter
period to infect volunteer plants. Mild or moist summers favour the
pathogen and inoculum is readily carried through for the next season. This is
the case for the mountains in Morocco, where occasional rain showers occur in
the summer.