Alternaria diseases of potatoes: epidemiology and management in Israel
D. Shtienberg
Department of Plant Pathology and Weed Research, ARO, the Volcani Center, Israel
Potato production in Israel
Cultivated area ~16,000 ha
Egypt
Jordan
Lebanon
Syria
Elat
Beer-Sheva
Tel-Aviv
Jerusalem
Haifa
Nazareth
25 km.
N
~500 ha in the north
~3,000 ha in the Sharon area
~12,300 ha in the northern Negev
~200 ha in the Arava
temperature
radiation
Tem
pera
ture
(oC
)
So
lar
rad
iati
on
(µ
E/m
2/m
in)
10
20
30
40
0
1000
2000
3000
Month of the year
VI X II VI
Autumn Spring
Potatoes are produced in Israel in two
growing seasons
Late blight – Phytophthora infestans
Early blight – Alternaria solani
Necrotic lesions – Alternaria alternata
Observations – early blight
1. The primary factor governing early blight intensity
is host physiology, as affected by the
environment;
2. The disease is intensified in senescing leaves
towards the end of the growing season.
pathogen
environment
host
disease
host
Vegetative stage
Conceptual model describing the changes in host response to early blight over time
tuberization
Ho
st
resp
on
se
Resist.
Sus.
emergence harvest
Using the conceptual model for describing differences among the two growing seasons
tuberization
Ho
st
resp
on
se
Resist.
Sus.
emergence harvest
From: Shtienberg et al. (1996) Plant Disease 80:994-998
Autumn season D
ise
as
e +
se
ne
sc
en
ce
severi
ty (
%) Spring season
Dis
ea
se
+ s
en
es
ce
nc
e
se
ve
rity
(%
)
Using the conceptual model for describing the response of cvs. with different maturity levels
tuberization
Ho
st
resp
on
se
Resist.
Sus.
emergence harvest
tuberization
Ho
st
resp
on
se
Resist.
Sus.
emergence harvest
Using the conceptual model for describing the response of cvs. with different genotype
resistance levels
No need to spray “supplementary” sprays
Using the conceptual model for describing the need for fungicide application
tuberization
Ho
st
resp
on
se
Resist.
Sus.
emergence harvest
Integrated management strategy for EB + LB
Components in the strategy
•the growing season (autumn or spring)
•genotype resistance (to EB and to LB)
•age related resistance (to EB)
•weather suitability (to EB and LB)
•fungicide type and efficacy
The goal: to effectively manage both diseases
emergence
Systemic against EB
Full rate protectant
Sprays against EB
Autumn season: management of EB
Host sus. to EB
No need to
spray
“supplementary” sprays
tuberization
Ho
st r
esp
on
se Resist.
Sus.
emergence harvest
emergence
Systemic against EB
Full rate protectant
Sprays against EB
Half rate protectant
A. no report of LB in the region
and LB Autumn season: management of EB
Host sus. to EB
emergence
Host sus. to EB
Systemic against EB
Full rate protectant
Sprays against EB
Half rate protectant
B. LB in the region but not in the field
and LB Autumn season: management of EB
LB in the region
Sprays against LB
emergence
Host sus. to EB
Systemic against EB
Full rate protectant
Sprays against EB
Half rate protectant
and LB Autumn season: management of EB
LB in the region
Sprays against LB
LB in the field
Systemic against LB
C. LB in the region and then in the field
0
1000
2000
3000
4000
1 5
Dis
ease
+ s
en
escen
ce
severi
ty (
AU
DP
C)
a
d
9
emergence
Host sus. to EB
Systemic against EB
Full rate protectant
Sprays against EB
Half rate protectant
Autumn
season
1997/8
LB in the region
Sprays against LB
LB in the field
Systemic against LB
2
b
9
c
4
5
3
bc
7
emergence
Systemic against EB
Full rate protectant Half rate protectant
Spring season: management of LB
Systemic against LB
emergence
Systemic against EB
Full rate protectant Half rate protectant
Spring season: management of LB
Systemic against LB
LB in the region
Sprays against LB
LB in the field
emergence
Systemic against EB
Full rate protectant Half rate protectant
Spring season: management of LB
Systemic against LB
Sprays against LB
LB in the field
LB in the region
0
250
500
750
1000
1250
1 5
Dis
ease
+ s
en
escen
ce
severi
ty (
AU
DP
C)
b
a
10
emergence
Systemic against EB
Full rate protectant Half rate protectant
LB in the field
Systemic against LB
LB in the region
Sprays against LB
Spring
season
1996
2
b
10
4
a
3
3
b
5
Necrotic lesions – Alternaria alternata
Observations
1. Necrotic lesions appear suddenly in large areas,
often after heavy rain events;
2.The phenomenon is more common in crops
growing in sandy soils;
3. Alternaria alternata was isolated from necrotic
lesions and the Koch postulates were completed
and proved the pathogenicity of that fungus.
Working hypothesis
1. Heavy rains wash the nitrogen fertilizer from the
root zone.
2. Necrotic lesions appear in plants suffering from
stress imposed by sudden reduction in nitrogen
content in the foliage.
pathogen
environment
host
disease
host
0
10
20
30
0 50 100 150 200 250
N - fertigation (kg/ha)
Nec
roti
c l
es
ion
se
ve
rity
(%
)
The interactive effects of N fertigation
on necrotic lesion severity
0
10
20
30
0 50 100 150 200 250
N - fertigation (kg/ha)
Nec
roti
c l
es
ion
se
ve
rity
(%
) No. of “rain” events
0
1. 33 DAP
1. 45 DAP
2. 33 and 45 DAP
The interactive effects of N fertigation and “rain”
on necrotic lesion severity
“rain” was mimicked by over head irrigation of 600 m3 water /ha
0
10
20
30
0 500 1000 1500 2000
N concentration in leaf petioles (ppm)
Ne
cro
tic
le
sio
n
se
ve
rity
(%
)
-6
-4
-2
0
0 500 1000 1500 2000
Y = -0.0018X – 1.6
r2 = 0.784; P < 0.01 Ne
cro
tic le
sio
n
se
ve
rity
(lo
git
)
Relationships between N concentration in leaf petioles and severity of necrotic lesions
0
10
20
30
40
- Rain
- N
Fungicide a
ab
b
The interactive effects of “rain”, supplemental N
fertigation, and fungicides, on necrotic lesion
Rain and supplemental N-fertigation
+ Rain*
- N
+ Rain
+ N**
Nec
roti
c l
es
ion
se
ve
rity
(%
) No
Yes*
* 4 tebuconazole sprays **180 kg N / ha *800 m3 water / ha
Take home messages 1. Early blight development is governed by host
physiology. Its management should relate to the
response of the host to the pathogen.
2. Early blight should be managed only in the
autumn season; Late blight - in both seasons.
3.Necrotic lesions develop primarily in nitrogen-
stressed plants. Applying supplemental N
fertilization reduces necrotic lesion severity.
4. Concepts for managing potato early and late blight
were developed, examined and found effective. The
concepts are implemented commercially by Israeli
growers for more than a decade.
Thank you for your attention