2008 Phytophthora Workshop in Italy

1. Flooding events and rising water temperatures
increase the significance of the reed pathogen Pythium phragmitis
Jan Nechwatal, Anna Wielgoss, Kurt Mendgen
Universität Konstanz, Phytopathology, Konstanz, Germany

2. Reed (Phragmites australis)
Perennial grass
Worldwide distribution
Littoral sites, up to 2m deep water
Economic value
Ecological value
www.BioLib.de

3. Reed (Phragmites australis)
Lake Constance (Bodensee)
Surface area 536 km²
Max. depth 254 m
Shore length 273 km
Max. length 63 km
Max. breadth 14 km

4. Reed Decline
Lake Constance reed belt area loss 1998-2000:
approx. 24 % (Germany)
from: Dienst & Schmieder, www.bodensee-ufer.de
Hypotheses:
- mechanical damage (recreation, boats, floating debris)
- water eutrophication
- animal feeding (insects, birds)
- reed damage shown to be related to flood duration, time and depth
- oxygen deficiency, anaerobic metabolism
„flood-induced reed dieback“ (Ostendorp, Dienst & Schmieder, 2003)

5. The Reed Pathogen: Pythium phragmitis
Nechwatal et al., 2005
sporangia oospores

6. The Reed Pathogen: Pythium phragmitis
Grass-associated clusters B1d and B1e
(Lévesque & de Cock, 2004)
Van der Plaats-Niterink, 1981
Nechwatal et al., 2005
P. arrhenomanes Drechsler (1928)

7. P. phragmitis: The Damage it Causes
oospore
© J.N.
… to seedlings
… to mature leaves
… no damage to roots and rhizomes infection mainly via leaves

8. P. phragmitis: The Role of Flooding Events
20 cm + P. phragmitis
– P. phragmitis
2000 ml
+ P. phragmitis
– P. phragmitis
25 plants (6-8 wks. old) per treatment

9. P. phragmitis: The Role of Flooding Events
1. plants fully submerged, all leaves below water line, 3 weeks
100
control
80
% live plants
60
40
20
Pythium
0
11 13 15 18 20 22
days post inoculation
Regeneration shooting, 2 wks. after harvesting (= 36 dpi)
Control: 5-8 cm per plant
Pythium: 0

10. P. phragmitis: The Role of Flooding Events
2. plants partly submerged, 50 or 75% of plant height, 4 weeks
50 Mean shoot length (live shoots)
40
30
[cm]
20
10 a b a b
0
%
%
0%
5%
50
75
l5
l7
50 % dead shoots
um
um
tro
tro
i
i
on
on
th
th
Py
Py
C
C
40
% dead shoots
30
20
10
0
%
%
0%
5%
75
50
l5
l7
m
m
ro
ro
hiu
hiu
nt
nt
t
co
Py
co
t
Py

11. P. phragmitis: The Role of Flooding Events
3. plants clipped before flooding to 6 or 12cm above soil line, 4 weeks
14 Mean regenerative shoot length, after 4 wks.
12
10
8
[cm]
6
4 a b a b
2
0
12
6
2
l6
l1
m
tro
m
tr o
iu
iu
on
th
on
th
Py
C
Py
C
Plant death, after 4 wks.:
Control 6: 0
Control 12: 0
Pythium 6: 36%
Pythium 12: 40%

12. P. phragmitis: The Role of Flooding Events
3. plants clipped before flooding to 6 or 12cm above soil line, 4 weeks
water level 12 cm
water level 6 cm
Nechwatal et al., 2008
control Pythium control Pythium

13. P. phragmitis: The Role of Flooding Events
flood
Schmieder et al., 2002: Limnologica 32, 131-146
Mean water level
1951-2000
- Reed damage shown to be related to flood duration, time and depth
- High susceptibility of submerged leaves to P. phragmitis
- No damage in the absence of the pathogen
P. phragmitis as a contributing factor in „flood-induced reed decline“

14. P. phragmitis: The Influence of Temperature
growth rate
35
30
25
20
mm/ d
15
10
5
0 Straile et al., 2003: Limnol. Oceanogr. 48, 1432–1438
6 15 19 25 30 33 37 40
temperature [°C]
10 20
leaf necrosis size zoospore production
Nechwatal et al., 2008: Hydrobiologia 613, 109-115
8
No. of infected bait ends
15
Lesion length [cm]
6
10
4
5
2
0 0
15 18 20 25 15 20 25
Temperature [°C] Temperature [°C]

15. P. phragmitis: The Influence of Temperature
30
young leaves flooded wind-bent, mature
plants flooded Logger 4 TÜ
Logger 8 Ü
25
Logger 1 T
Logger 2 T
Logger 3 T
20 Logger 6 Ü
°C
15
10
5
0
August
August
August
Nov
Nov
Nov
Juni
Juni
Juni
Juli
Juli
Juli
März
März
März
Dez
Dez
Dez
Jan
Jan
Jan
Jan
April
April
April
Sept
Sept
Sept
Okt
Okt
Okt
Mai
Mai
Mai
Temperature logger data 2005 (littoral water and sediment)
Mean temperature above 15°C ≈ mean highest lake water line (June – Sept.)
optimum infection conditions

16. Flooding events and rising water temperatures
increase the significance of the reed pathogen Pythium phragmitis
- Pythium phragmitis as an aggressive pathogen of common reed
- seedlings as well as mature leaves are susceptible
- negative impact of flooding on reed only in the presence of the pathogen
- flooding periods often equal periods of optimum temperature for the pathogen
- optimum infection conditions
- loss of plant vigour
- losses in reed belt area
- symptoms of reed decline
-`climate change`: effect on flooding events (earlier in the year – younger plants!)
-`climate change`: temperature effect on pathogen (growth, sporulation, virulence)

17. Thank you …
‚Littoral Zone of Lake Constance‘
The role of fungi during development and decay of reed (Phragmites australis)