1.4 Assessment of yield losses imposed by plant pathogens Introduction and definitions Effects of...
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1.4 Assessment of yield losses imposed by plant pathogens
•Introduction and definitions
•Effects of plant pathogens on host physiology
•Effects of plant pathogens on yield and its components
•Models for loss assessment
•Concluding remarks
Time
Dis
ease
inte
nsi
ty
Time
Yie
ld Loss prediction
Why do we need (want) to assess yield loss?or
What are the uses of yield loss records
•For identifying the time when control is needed and assisting to develope effective management procedures.
•For making decision concerning the need of disease management (cost/effective calculations).
Why do we need (want) to assess yield loss?or
What are the uses of yield loss records
•For administrative decisions: making priorities in research, breeding, allocation of efforts, etc.
•For insurance purposes.
Time
Dis
ease
inte
nsi
ty
Time
Yie
ld
Loss assessment
Loss assessments can be made on several scales:
•Individual plants
•Small plots (e.g., experimental plots)
•Individual field
•Regions
•Nations
•The entire world
How plant pathogens affect their hosts ?
Effects on host physiology
Effects on host development
Effects on yield quantity
Effects on yield quality
Leaf infection
Effects on host physiology
Effects on host development
Effects on yield quantity
Effects on yield quality
Stem infection
How plant pathogens affect their hosts ?
Effects of plant pathogens on their hosts
Effects on yield quantity
Effects on yield quality
Fruit rotEffects on host development
Effects on host physiology
Effects on host physiology
Effects on yield quantity
Effects on yield quality
Fruit ghost spotsEffects on host development
How plant pathogens affect their hosts ?
Effects of plant pathogens on host physiology
•Effects of radiation interception (RI)
•Effects of radiation use efficiency (RIE)
reflected radiation
intercepted radiation
transmitted radiation
Effects of plant pathogens on host physiology
Effects of radiation interception
Stand reducers
Seedling diseases
Effects of plant pathogens on host physiology
Effects of radiation interception
Tissue consumers
Alternaria macrospora in cotton
Effects of plant pathogens on host physiology
Effects of radiation interception
Leaf senescence accelerators
Alternaria solani in tomatoes
Effects of plant pathogens on host physiology
Effects of radiation interception
Light “stealers”
Smutty mold (Aspergillus sp.) in cotton
Disease severity (%) P
hot
osyn
thes
is r
ate
(%)
0 50 1000
50
100
invaded area
infected area Necrotic area
Effects of plant pathogens on host physiology
Effects of radiation use efficiency
photosynthetic rate reducers
Effects of plant pathogens on host physiology
Effects of radiation use efficiency
Turgor reducers
Disease severity (%)
Tra
nsp
irat
ion
rat
e (%
)
0 50 1000
50
100
stomata
Alternaria
stomata
Effects of radiation use efficiency
Turgor reducers
Disease severity (%)
Tra
nsp
irat
ion
rat
e (%
)
0 50 1000
50
100
Powdery mildew
stomata
Effects of radiation use efficiency
Turgor reducers
Disease severity (%)
Tra
nsp
irat
ion
rat
e (%
)
0 50 1000
50
100rusts
stomata
rust pustules
Effects of Alternaria macrospora on cotton yield(mean of 11 field experiments)
Treatment yield (t/ha) yield increment
t/ha %
UntreatedManeb
4.265.03
-0.78
-15.4
Tebuconazole 5.70 1.44 25.2
Measurement of yield loss: which reference to use?
Commercially managed-plot yield
(t/ha)Untreated-plot yield 3.0
5.0
Attainable yield 8.0
Potential yield 15.0
-40%
+66%
Healthy-plot yield 6.0-50%
+100%
Measurement of yield loss: what is the reference?
Differences between yield of a reference plot and yield of a diseased plot
Loss = [yield of reference plot] - [yield of diseased plot]
Reference plots:
A non-infected (healthy) plot
The least infected plot in the experiment
Average yield of commercial plot in the area
Measurement of yield loss: what is the reference?
Differences between estimated yield of a healthy plot and yield of a diseased plot
Loss = [estimated yield of healthy plot] - [yield of diseased plot]
Disease severity (%)
Yie
ld (
t/h
a)
0 100
The damage function
The quantitative relationship between disease intensity and yield (or yield loss)
Disease intensity ( %)
Yie
ld (
t/h
a)
Disease intensity ( %)Y
ield
loss
(%
)
The damage function
Disease intensity
Yie
ld
Linear
Disease intensity
Yie
ld
Logarithmic
Disease intensity
Yie
ld
Compensation
Disease intensity
Yie
ld
Optimum
Yield components of cereals
no. of spikelets per ear
no. of spikelets per unit area
no. of grains per spikelet
no. of grains per unit area
Yield per unit area
weight of a grain
no. of plants per unit area
no. of ears per plant
no. of ears per unit area
The yield components that are affected by plant diseases are those that are created at, or
soon after, the time of disease onset
% difference
No. of ears/plant
No. spikelets/ear
Grain wt.
Yield
19.1*
7.6
4.2
28.5*
Growth stage
tillering
Dis
ease
sev
erit
y (%
)
untreated
sprayed
emergence
Effects of powdery mildew in barley on yield and its components
milk
Growth stage
tillering
Dis
ease
sev
erit
y (%
)
Effects of Septoria tritici blotch in wheat
on yield and its components
untreated
sprayed
earing
% difference
No. of ears/plant
No. spikelets/ear
No. grains/spikelet
Grain weight
Yield
2.5
0.8
8.1*
8.0*
18.1*
In Israel, Septoria tritici blotch in wheat affects only the weight of individual grains.
Thus, there is no need to control the disease before the earing stage.
Similarly, the is no need to control the disease after most of the grain weight was accumulated.
Yield components of a board-leaf plant
Emergence
Vegetative growth
Reproductive growth
Yield production
Yield components of a broad-leaf plant
weight of individual fruit
Yield per unit area
no. of plants per unit area
no. of fruits per plant
no. of fruits per unit area
Effects of Alternaria in cotton on yield and its componentsB
oll w
eigh
t
Bol
l Nu
mb
er
untreated
sprayedYie
ld
A. macrospora affect only the number of bolls per plant.
Bolls are shed only at the initial stages of their development.
Thus, disease management is very important early in the season when the bolls are small, but not towards the end of the season, when the bolls had already developed enough.
The critical point model
Disease severity at time G1 (%)
Yie
ld (
t/h
a)
Time
Dis
ease
sev
erit
y (%
)
G1
harvest
disease assessment
Y = 0- 1X
Y = yield of a diseased plot 0 = estimated yield of a healthy plot1 = reduction in yield for each percent increase in disease severity X = disease severity of the diseased plot
The critical point model is used mainly in cereals.
In cereals have distinct growth stages and it is possible to determine precisely which crop growth stage is affected most by the disease.
This stage should be chosen to be the “critical” stage - for assessment.
Critical point models are used mainly for “after-season” loss assessment.
Uses of critical point models
The multiple point model
Time
Dis
ease
sev
erit
y (%
)
T1 T2 T3 T4 T5 T6T7 T8
Y = 0- 1X1 - 2X2 - 3X3 - 4X4 - 5X5 - 6X6 - 7X7 - 8X8
Y = yield of a diseased plot 0 = estimated yield of a healthy plot1-8 = reduction in yield in each sampling for each percent
increase in disease severity X1-X8 = disease severity of the diseased plot in each date
harvest
disease assessments
The multiple point model is used mainly in broad-leaf crops.
In broad-leaf crops yield is accumulated during a long period and there are no distinct growth stages.
In many cases, the disease affect yield during the whole period of its accumulation.
Multiple point models are used mainly for “after-season” loss assessment.
Uses of multiple point models
Time
Dis
ease
sev
erit
y (%
)
T1 T2 T3 T4
Critical severity
The critical time model
Time for critical severity (days)Y
ield
(t/
ha)
Y = 0+ 1X
Y = yield of a diseased plot 0 = estimated yield of a plot infected at day 01 =increase in yield for each day of delay in time to critical severity X = time for critical severity in diseased plot
Critical time models may be used in both cereals and broad-leaf crops.
These models are applicable in situations where disease onset vary markedly from year to year and from location to location.
The critical time models may be used for decision making. For that purpose, the critical severity level to be used should be low enough, to enable proper disease suppression.
Uses of critical time models
The Area Under the Disease Progress Curve (AUDPC) model
Time
Dis
ease
sev
erit
y (%
)
AUDPC (Disease*days)
Yie
ld (
t/h
a)Y = 0- 1X
Y = yield of a diseased plot 0 = estimated yield of a healthy plot1 =decrease in yield for each increase in AUDPC unit X = AUDPC units
The AUDPC models are used in both broad-leaf and cereal crops.
In most cases, a very good relationship exist between AUDPC values and yield.
The AUDPC models are used mainly for “after-season” loss assessment.
Uses of the AUDPC models
Concluding remarks•Losses may be predicted early in the season for management decision making or after the season for general analyses.
• Plant pathogens may affect the physiology of the host and result in yield losses directly or indirectly.
•Determination of the yield component to be affected by the disease is an important component of an IPM strategy.
•Yield loss should be determined in relation to a reference plot.
•Yield loss may be quantified by several models: the critical point model, the multiple point model, the critical time model and the AUDPC model.