1.4 Assessment of yield losses imposed by plant pathogens Introduction and definitions Effects of plant pathogens on host physiology Effects of plant pathogens

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 development



Stem infection


Effects of plant pathogens on their hosts



Fruit rotEffects on host development





Fruit ghost spotsEffects on host development



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 radiation interception

Stand reducers

Seedling diseases



Tissue consumers

Alternaria macrospora in cotton



Leaf senescence accelerators

Alternaria solani in tomatoes



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 radiation use efficiency

photosynthetic rate reducers



Turgor reducers

Disease severity (%)

Tra

nsp

irat

ion

rat

e (%

)

0 50 1000

50

100

stomata

Alternaria

stomata


Turgor reducers


Tra

nsp

irat

ion

rat

e (%

)

0 50 1000

50

100

Powdery mildew

stomata


Turgor reducers


Tra

nsp

irat

ion

rat

e (%

)

0 50 1000

50

100rusts

stomata

rust pustules


assimilate suppers

Powdery mildews

Quantification of yield losses

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]


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

The relationship between the time of disease development

and the resultant yield loss

Yield components of cereals

Emergence

Tillering

Boot stage

Grain filling

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.

Yield loss models

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.

Documents

1.4 Assessment of yield losses imposed by plant pathogens Introduction and definitions Effects of plant pathogens on host physiology Effects of plant pathogens