1. Models for estimate yield losses due to wheat rusts and powdery mildew By Dr.Gamalat Abd-Elazize& Dr. Mohamed Abdelkader Wheat Diseases Research Department

2. Introduction
Wheat is one of the most significant crops, with total production about 610 million tones annually.
Diseases, insects, and weeds are a major constraint to crop production worldwide they can destroy between 31-42% of all crops annually.
The damage depends on the severity and time of infection.
Approximately 14% of these losses are due to diseases which amount to about US$220 billion dollars annually.
Rust diseases are the most important diseases of cereals followed powdery mildew. They can cause up to 60% loss of yield for leaf rust, yellow rust, powdery mildew and 100% for stem rust.
In 1995 wheat strip rust caused yield losses ranged from 14 to 26% in delta region in Egypt, while the national loss was about 10%.
Estimates of yield losses of cereals caused by rusts since 1918 are maintained by the United States Department of Agriculture Research Service Cereal Disease Laboratory in St. Paul, Minnesota.

3. Why we estimate yield loss
To evaluate the genetic level of resistance in a variety.
To estimate the economic significance of the disease by relating the disease infection to yield loss.
To determine the economic threshold at which the control measurement is applied.
Losses can be divided to
Indirect losses
during harvesting
Direct losses
caused by diseases
Shriveled grain
Reduction in number

5. Yield losses estimation
Doling and Doodson: correlated between disease severities during flowering stage and yield loss with the following equations:
loss = 0.268x disease severity ( R )+3.9
loss = ( 3.01x the square root of disease severity)-3.6
Mondy et. al.,: correlated between final disease severity stage and yield loss with the following equations:
loss = 0.44x disease severity ( R )+3.15
loss = ( 5.06x the square root of disease severity)-17.15
Calpuza et. al., Yd
loss % = x Where; Yd = yield of diseased plants
Y h Y h = yield of healthy plants

6. Relation between wheat disease severity, wheat growth stage, and percentage yield loss.
Stem rust %
Yield
loss
Ripe
Late
dough
Early
Milk
Flower
Boot
0.0 5
trace -
0.5 10
5.0 25
15.0 40
50.0 65
75.0
100
100.0

7. Relationship between area under disease progresses curve (AUDPC) and yield loss AUDPC = D[1/2(y1+yk)+(y2+y3+…..+yk-1)] Where; y1,y2,y3,…..and yk = disease scores D = days between two consecutive recording

8. Area under the curve model
These type of assessment method based on the area under disease progress curve.
The experiment should be conducted over a period at least 3years , large plots should be used where possible, using the normal farming system to create an epidemic. Plots must be surrounded with highly susceptible check (border).
Artificial inoculation were don at the border with rusts or powdery mildew diseases once or twice.
In any design, the disease is allowed to develop in some plants and controlled in others( healthy treatments).

9. Data collection and data analyses
Severity of rusts or powdery mildew were assessed many times (4-5) records.
Total yield (yield per plot) harvested with discarded the first and the last raw.
Single plants according to the disease severity can be selected randomly in each plot and lagged and harvested separately.
Yield components i.e., yield per plot, yield per plant, kernel weight.
The data statistically by MSTAT program .
Regression coefficient (R2) were calculated among disease variables and yield components.

10. loss model -a
Graphs showing relationship between number of tiller, 500-kernel weight and area under powdery mildew progresses curve
R2 =0.60
R2 =0.44

11. loss model -b
Graph showing relationship between number of kernels/plant and area under powdery mildew progresses curve
R2=0.87

12. Loss model -c
Relationship between AUDPC and maximum yield (Total yield)
100 grain samples
Infected
Healthy
R2=0.52

13. THANK YOU