Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue8-9.Aug2000:

Soil Biology & Biochemistry 32 (2000) 1141±1150
www.elsevier.com/locate/soilbio

Abiotic characteristics of soils suppressive to Aphanomyces root
rot
Lars Persson a,*, S. Olsson b
a

Plant Pathology and Biocontrol Unit, SLU, P.O. Box 7035, S-750 07 Uppsala, Sweden
b
Department of Quaternary Geology, TornavaÈgen 13, S-223 63 Lund, Sweden

Abstract
Soils showing suppressiveness to Aphanomyces root rot of pea in bioassays and ®eld experiments were surveyed in an area
intensively cultivated with vining pea in southern Sweden. By examining the relationships between disease suppression, soil
mineralogy, and selected physicochemical properties of 24 soils with di€erent degrees of suppressiveness, the suppressive soils
could be divided into two groups, mainly on the basis of their textural characteristics. Both soil groups are developed in
unsorted sediments. The ®rst group, S1, consisted of soils with a low content of clay (9±12%), and a high content of sand (56±
73%). The second group, S2, consisted of soils with a clay content of 19±21%, high pH (>6.7), and a high content of calcium
(>17 cmol kgÿ1). The ratio of the peak intensity of vermiculite±smectite to the peak intensity of illite±kaolinite in the X-ray
di€ractograms was high in these soils, and an increase in disease suppression was closely related to an increase in this ratio.

There were also signi®cant correlations between disease suppression on one hand and content of clay, calcium and pH on the
other. The results suggest that soils disease suppressive to Aphanomyces root rot can be found by searching for soils with
speci®c abiotic characteristics. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Aphanomyces euteiches; Pea; Disease suppression; Clay mineral; Clay content

1. Introduction
Aphanomyces euteiches Drechs. is a soil-borne
pathogen that causes root rot of pea (Pisum sativum
L.). There are no e€ective methods, such as plant resistance or fungicides, available for disease control.
The only practical method for reducing losses is to
avoid ®elds with a high infestation of the pathogen.
Recent studies, however, have shown that soils
strongly suppressive to the disease occur in southern
Sweden. In these soils, disease severity remains low
despite the presence of the pathogen and suitable climatic conditions for infection. The suppressiveness was
measured in a bioassay and was con®rmed in ®eld ex-

* Corresponding author. Findus R&D, Box 520, S-267 25 Bjuv,
Sweden. Tel.: +46-42-86683; fax: +46-42-81649.
E-mail address: lars.persson@rdbj.nestle.com (L. Persson).

periments with pea monocultures on suppressive and
conducive soils (Persson et al., 1999). Suppressiveness
to Aphanomyces root rot has been studied in only a
few earlier investigations (e.g. Oyarzun et al., 1997),
but soils suppressive to other diseases caused by, for
example, Fusarium spp., Chalara elegans Nag Raj and
Kendrick (synonamorph = Thielaviopsis basicola
(Berk and Broome) Ferraris), Histoplasma capsulatum
Darling, and Pythium spp., have been found and investigated in several places (Alabouvette et al., 1979;
Scher and Baker, 1980; Stotzky and Martin, 1963;
Stotzky and Post, 1967; Stutz et al., 1989). In several
of these cases, various microorganisms appear to act
as antagonists against the pathogen, but in addition,
suppressiveness is often related to various physicochemical properties of the soil (HoÈper and Alabouvette, 1996; Stotzky, 1986). Some investigations of
disease-suppressive soils have revealed involvement of
certain clay minerals in disease suppression (Stotzky

0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 3 0 - 4

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L. Persson, S. Olsson / Soil Biology & Biochemistry 32 (2000) 1141±1150

and Martin, 1963; Stotzky and Post, 1967; Stutz et al.,
1989). Amendments with clay minerals of the smectite
group, such as montmorillonite, have been shown to
enhance respiration of bacteria and to increase disease
suppression in a conducive soil and also to increase
the antagonism towards certain fungi by bacteria
(Amir and Alabouvette, 1993; Rosenzweig and
Stotzky, 1979; Stotzky 1966a,1966b, 1986; Stotzky and
Rem, 1966). Further, soils suppressive to diseases
caused by Phytophthora spp. and Pythium spp. often
have larger contents of organic matter, and disease
suppressiveness to these diseases can be induced by
amendment with, for example, composts (Broadbent
and Baker, 1974; Hoitink et al., 1996).
The objective of this investigation was to study possible relations between the suppression of Aphanomyces

root rot, as evaluated in a bioassay and/or in pea
monoculture ®eld experiments, and selected physicochemical properties of the soils tested.

2. Materials and methods
2.1. Soil sampling and assessment of disease suppression
The disease suppressiveness of soil samples collected
from ®elds in the area of vining pea production in

Fig. 1. Map showing the geographic distribution and geologic classi®cation of the soils used (clayey tills = clay content, 5±15%; clay
tills = clay content, 15±25%).

southern Sweden was assessed in a bioassay, as previously described by Persson et al. (1999). Based on
preliminary results and observations showing a relation between disease suppression and soil type, soil
samples were collected from 24 representative ®elds of
the most common soil types in the area. Soils sampled
within the study area have developed in Weichselian
glacial deposits of various genesis (Fig. 1; Table 1).
Water-deposited sediments of sand, silt or clay dominate on the lowland areas of region 1 (Fig. 1), whereas
unsorted glacial sediments (tills) are dominant in the
rest of the study area. The lithological character of the

latter sediments is strongly controlled by the composition of the bedrock, which is complex with a mosaic
of di€erent rocks at the surface of the bedrock. Inheritance from the local bedrock of Mesozoic, loose clay
and sandstones has resulted in mainly sandy or silty,
clayey tills (clay content 5±15%) and clay tills (clay
content 15±25%) in the north-western part of the
study area (3 in Fig. 1). Tills in the eastern part (2 in
Fig. 1) normally have lower clay content and high frequencies of Palaeozoic shales and acid magmatic
rocks. The south-western part (4 in Fig. 1) is dominated by calcareous clay tills with a high admixture of
Cretaceous and Tertiary chalk and limestones from the
local bedrock.
Soil samples were collected in the summer. Fields
with a high natural infestation of A. euteiches were
avoided if possible, to avoid in¯uence on the results of
the bioassay. About 10 subsamples, taken to a depth
of 20 cm and mixed to give a general sample, were collected from an area of 5  5 m. Samples were stored in
plastic bags at 48C and used in the bioassay within six
days. In the assessment of disease suppression, the
soils were inoculated with a dry oospore±talcum inoculum (800±1000 oospores mlÿ1 of soil), giving a disease
severity index (DSI) of about 75 in a conducive reference soil, as described by Persson et al. (1999). The
inoculated soils were incubated in a growth chamber

for seven days, then sown with 10 pea seeds of the cultivar ``Tristar'' treated with metalaxyl (Apron 200 LS,
20% a.i.) and watered daily to give optimal conditions
for infection (Persson et al., 1999). Six replicates of
each soil were used in the bioassay. After four weeks,
the roots of the pea plants were examined, and each
plant was assigned a DSI as follows: 0 = healthy
plant without any symptoms; 5 = discoloration of less
than 5 mm on a single root; 10 = discoloration of
about 20 mm of the root system; 25 = about 50% of
the root system was dark and a€ected; 50 = the whole
root system was dark and a€ected; 75 = the whole
root system, as well as the epicotyl, was dark and
a€ected; and 100 = dead plant (Persson et al., 1997).
An average DSI was then calculated for each tested
soil.
The ®eld relevance of disease suppressiveness

Table 1
Disease severity index (DSI) of soils from di€erent areas inoculated with oospores of Aphanomyces euteiches in a bioassay and selected physicochemical properties of the soils
Areaa

DSI

Clay (%)

Silt (%)

Sand (%)

Cb (%)

pHc

Cad (cmol kgÿ1)

Mgd (cmol kgÿ1)

Kd (cmol kgÿ1)

Groupe

4608
1616
4612
4615
R8
1617
82f
83f
80f
87
81f
85C
L350
85Sf
4517
H511
L553
84f
4529

4534
1521
1615
1613
1611

2
1
2
2
3
1
3
3
3
3
3
3
4
4

4
4
4
4
4
1
1
1
1
1

5
49
21
29
76
18
66
77
58

73
35
46
5
20
16
14
3
27
20
99
78
73
81
65

9
9
9
10
11
12
12
13
15
15
16
17
19
19
20
21
21
21
21
35
35
40
41
41

18
38
34
30
36
28
39
35
39
34
40
44
28
38
31
37
44
36
44
32
18
40
48
54

73
47
56
58
45
59
48
44
44
50
40
39
51
35
48
39
31
41
34
30
45
19
7
3

1.87
2.06
2.96
1.63
1.22
5.54
1.16
1.19
1.49
1.28
1.68
1.68
1.93
1.81
1.26
1.87
1.39
1.33
2.04
1.65
1.95
2.14
2.25
2.23

6.2
6.8
8.0
6.1
6.2
6.5
6.2
6.9
6.6
6.5
7.2
7.6
7.9
7.7
8.0
7.9
7.5
7.3
6.8
8.1
7.4
7.0
6.7
6.0

5.5
8.5
18.0
9.0
6.0
12.5
5.5
10.0
11.0
8.5
14.0
13.0
36.4
17.5
31.9
32.9
19.5
18.0
22.0
35.4
22.0
20.0
16.0
16.0

0.3
0.4
3.0
0.3
0.5
0.6
0.3
0.8
0.6
0.5
0.5
0.8
0.9
0.8
1.0
0.6
0.6
0.7
1.2
3.0
1.9
2.0
1.5
1.7

0.1
0.1
0.3
0.3
0.5
0.2
0.4
0.3
0.3
0.2
0.2
0.5
0.3
0.2
0.4
0.4
0.3
0.3
0.4
0.7
0.4
1.0
0.5
0.8

S1

a

Sampling area (Fig. 1), 1 = glaci¯uvial deposits, glacial/post-glacial clays; 2 = sandy clayey tills; 3 = clayey tills, clay tills; 4 = clay tills.
% Organic carbon, dry-weight basis.
c
H2O 1.0:2.5, soil:H2O.
d
Ammonium lactate extractable.
e
Group of suppressive soil, i.e. DSI R 30. S1 = sampled in area 1 and 2; S2 = sampled in area 4.
f
Pea monoculture ®eld experiments performed.

S1
S1
S1

S2
S2
S2
S2
S2
S2
S2

L. Persson, S. Olsson / Soil Biology & Biochemistry 32 (2000) 1141±1150

Soil

b

1143

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L. Persson, S. Olsson / Soil Biology & Biochemistry 32 (2000) 1141±1150

measured in the bioassay was assessed in six ®eld experiments with pea grown in monoculture for four
consecutive years. The experiments were located in
®elds ranging from low to high in soil suppressiveness
to pea root rot according to the bioassay, and the
results indicated a good relation between the suppressiveness in the bioassay and in the ®eld (Persson et al.,
1999). Each experiment consisted of four plots, each 3
 10 m, located beside each other. The infection of A.
euteiches in the ®eld experiments was assessed by
counting the number of oospores in pea roots (Persson
et al., 1999). Each year, at the beginning of the ¯owering stage, 10 plants were collected from a depth of approximately 20 cm at four randomly chosen places in
each plot. The roots were cut into pieces and comminuted in water with a dispersing machine (Polytron,
Kinematica AG, Littau, Switzerland), the oospore concentration in the slurry was counted using a hemacytometer and the number of oospores gÿ1 of root fresh
weight was calculated.
2.2. Determination of soil properties
Particle size analysis was done by standard sieving
and hydrometer methods (Gandahl, 1952). The contents of organic and inorganic carbon were determined
by heating dried and homogenized samples from
1008C to 10008C in a Leco furnace (RC 412). The output from the CO2-detector of the instrument was
recorded continuously, which allowed the sources of
carbon to be di€erentiated by the temperature at
which they oxidized/volatilized. Soluble potassium,
magnesium, and calcium were determined by extraction with acid ammonium lactate (pH 3.75; SIS, 1993).
The pH of fresh soil was determined potentiometrically
in water (1.0:2.5, soil:water, w/w).
2.3. Determination of clay mineralogy
Analysis of the clay mineralogy was done on 12 of
the 24 soil samples, representing the most common soil
types of the area. The mineralogical composition of
the clay fraction (