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

Reed (Phragmites australis)

Perennial grass

Worldwide distribution

Littoral sites, up to 2m deep water

Economic value

Ecological value

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w.B

ioLi

b.de

Reed (Phragmites australis)

Lake Constance (Bodensee)Surface area 536 km²Max. depth 254 mShore length 273 kmMax. length 63 kmMax. breadth 14 km

from

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Lake Constance reed belt area loss 1998-2000: approx. 24 % (Germany)

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)

Reed Decline

The Reed Pathogen: Pythium phragmitis

sporangia oospores

Nec

hwat

al e

t al.,

200

5

P. arrhenomanes Drechsler (1928)

The Reed Pathogen: Pythium phragmitis

Grass-associated clusters B1d and B1e(Lévesque & de Cock, 2004)

Van

der

Pla

ats-

Nite

rink,

198

1

Nec

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200

5

© J.N.

… to seedlings

P. phragmitis: The Damage it Causes

oospore

… to mature leaves

… no damage to roots and rhizomes infection mainly via leaves

25 plants (6-8 wks. old) per treatment

2000 ml

20 cm

P. phragmitis: The Role of Flooding Events

+ P. phragmitis– P. phragmitis

+ P. phragmitis– P. phragmitis

0

20

40

60

80

100

11 13 15 18 20 22

days post inoculation

% li

ve p

lant

s

Regeneration shooting, 2 wks. after harvesting (= 36 dpi)Control: 5-8 cm per plantPythium: 0

1. plants fully submerged, all leaves below water line, 3 weeks

control

Pythium

P. phragmitis: The Role of Flooding Events

2. plants partly submerged, 50 or 75% of plant height, 4 weeks

0

10

20

30

40

50

Contro

l 50%

Pythium

50%

Contro

l 75%

Pythium

75%

[cm

]

Mean shoot length (live shoots)

0

10

20

30

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50

contr

ol 50

%

Pythium 5

0%

contr

ol 75

%

Pythium 75

%

% d

ead

shoo

ts

% dead shoots

a ab b

P. phragmitis: The Role of Flooding Events

3. plants clipped before flooding to 6 or 12cm above soil line, 4 weeks

0

2

4

6

8

10

12

14

Contro

l 6

Pythium 6

Contro

l 12

Pythium 12

[cm

]

Mean regenerative shoot length, after 4 wks.

Plant death, after 4 wks.:Control 6: 0Control 12: 0Pythium 6: 36%Pythium 12: 40%

a ab b

P. phragmitis: The Role of Flooding Events

water level 12 cm

water level 6 cm

control Pythium control Pythium

3. plants clipped before flooding to 6 or 12cm above soil line, 4 weeks

P. phragmitis: The Role of Flooding Events

Nec

hwat

al e

t al.,

200

8

Sch

mie

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200

2: L

imno

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ca 3

2, 1

31-1

46

- 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“

flood

Mean water level1951-2000

P. phragmitis: The Role of Flooding Events

0

5

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6 15 19 25 30 33 37 40temperature [°C]

mm

/ d

growth rate

Straile et al., 2003: Limnol. Oceanogr. 48, 1432–1438

0

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4

6

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15 18 20 25

Temperature [°C]

Lesi

on le

ngth

[cm

]

leaf necrosis size

0

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15 20 25

Temperature [°C]

No.

of i

nfec

ted

bait

ends

zoospore production

P. phragmitis: The Influence of Temperature

Nec

hwat

al e

t al.,

200

8: H

ydro

biol

ogia

613

, 109

-115

0

5

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30M

ärz

Mär

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ärz

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aiM

ai

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Juli

Juli

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ust

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ept

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Jan

°C

Logger 4 TÜ

Logger 8 Ü

Logger 1 T

Logger 2 T

Logger 3 T

Logger 6 Ü

Temperature logger data 2005 (littoral water and sediment)

Mean temperature above 15°C ≈ mean highest lake water line (June – Sept.)optimum infection conditions

P. phragmitis: The Influence of Temperature

young leaves flooded wind-bent, matureplants flooded

- 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)

Flooding events and rising water temperatures increase the significance of the reed pathogen Pythium phragmitis

‚Littoral Zone of Lake Constance‘

The role of fungi during development and decay of reed (Phragmites australis)

Thank you …