Identification and pathogenicity of Rhiz
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Identification and pathogenicity of Rhizoctonia species isolated from bean
and soybean plants in Samsun, Turkey
Ismail Erpera; Ibrahim Ozkocb; Gürsel Hatat Karacac
a
Plant Protection Department, Agriculture Faculty, Ondokuz Mayis University, Samsun, Turkey b
Biological Sciences Department, Faculty of Arts and Sciences, Samsun, Turkey c Plant Protection
Department, Agriculture Faculty, Süleyman Demirel University, Isparta, Turkey
Online publication date: 25 January 2011
To cite this Article Erper, Ismail , Ozkoc, Ibrahim and Karaca, Gürsel Hatat(2011) 'Identification and pathogenicity of
Rhizoctonia species isolated from bean and soybean plants in Samsun, Turkey', Archives Of Phytopathology And Plant
Protection, 44: 1, 78 — 84
To link to this Article: DOI: 10.1080/03235400903395427
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Archives of Phytopathology and Plant Protection
Vol. 44, No. 1, January 2011, 78–84
Identification and pathogenicity of Rhizoctonia species isolated from
bean and soybean plants in Samsun, Turkey
Ismail Erpera*, Ibrahim Ozkocb and Gürsel Hatat Karacac
a
Plant Protection Department, Agriculture Faculty, Ondokuz Mayis University, Samsun,
Turkey; bBiological Sciences Department, Faculty of Arts and Sciences, Samsun, Turkey; cPlant
Protection Department, Agriculture Faculty, Süleyman Demirel University, Isparta, Turkey
Downloaded By: [TÜBTAK EKUAL] At: 12:03 26 January 2011
(Received 11 September 2009; final version received 24 September 2009)
A total of 434 isolates of Rhizoctonia belonging to 10 anastomosis groups were
obtained from the roots and rhizosphere soils of bean and soybean plants grown in
Samsun, Turkey. AG-4 was found to be the most common group on bean and
soybean plants and AG-5, AG-6, binucleate AG-A, AG-B and R. zeae were other
groups isolated from the both plant species. AG-1, AG-7 and AG-K from bean
and AG-E from soybean were other groups obtained in the study. The
pathogenicity tests on bean and soybean seedlings showed that the highest disease
severities were caused by AG-4 isolates, whereas AG-1 and AG-6 isolates were
moderately pathogenic. Binucleate Rhizoctonia AG-B isolates were also moderately pathogenic, while other binucleate Rhizoctonia were found to be weakly
pathogenic. Rhizoctonia zeae isolates caused moderate disease symptoms on bean,
but soybean plants were slightly affected by this group of isolates. This is the first
reported observation of R. solani AG-6 and AG-7 and binucleate Rhizoctonia AGB on bean, and R. solani AG-5 and AG-6 and binucleate Rhizoctonia AG-A, AG-B
and AG-E on soybean, in Turkey.
Keywords: Rhizoctonia; Phaseolus vulgaris L.; Glycine max L.; anastomosis group;
pathogenicity
Introduction
Bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) are the major legume
crops grown in Samsun, Turkey. Especially, bean is very common in the province,
and with its 105.436 tones production Samsun comes first in our country. Soybean is
the second important legume plant in the province with 11.598 tones production
(Anonymous 2003). Because of the warm and humid weather conditions of the
province, mainly fungal diseases can cause significant yield losses. Among those,
damping off and root rot is very common on legume crops, and Rhizoctonia group
fungi were found to be one of the main agents of the disease (Ecevit et al. 1988).
These fungi are among the soil-borne pathogens, which attacks a wide range
of plants and are distributed all over the world (Ogoshi 1996). R. solani Kühn
[teleomorph: Thanatephorus cucumeris (Frank) Donk.] and binucleate Rhizoctonia
(teleomorph: Ceratobasidium Rogers) are divided into anastomosis groups (AGs)
based on hyphal anastomosis reactions between isolates. R. solani is composed of
*Corresponding author. Email: ismailer@omu.edu.tr
ISSN 0323-5408 print/ISSN 1477-2906 online
Ó 2011 Taylor & Francis
DOI: 10.1080/03235400903395427
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Archives of Phytopathology and Plant Protection
79
13 AGs designated as AG-1 to AG-13 (Sneh et al. 1991; Carling et al. 2002;
Woodhall et al. 2007). Only 16 Binucleate Rhizoctonia AGs are currently known
(Sharon et al. 2008). Rhizoctonia zeae and Rhizoctonia oryzae were accepted as
anamorphs of Waitea circinata (Leiner and Carling 1994).
Among Rhizoctonia group fungi, R. solani is the most common and virulent
species and can cause several types of damage, including hypocotyl rot, root rot and
web blight on bean (Galindo et al. 1983; Sumner 1985), and damping-off, root rot,
stem rot, and foliar blight on soybean (Sinclair and Backman 1989). AG-4 is the
major AG worldwide, causing root rot on bean. However, other AGs (AG-1, AG-1IB, AG-2-1, AG-2-2 and AG-5) have also been reported on bean (Muyolo et al.
1993; Echavez-Badel et al. 2000). In Turkey, some R. solani (AG-1, AG 2-1, AG 2-2,
AG-3, AG-4, AG-5, AG-9, AG-10 and AG-11) and binucleate Rhizoctonia AGs
(AG-A, AG-E, AG-F, AG-G, AG-I and AG-K) have previously been recognized
on bean (Demirci and Döken 1995; Karaca et al. 2002; Eken and Demirci 2004).
R. solani AGs reported on soybean were AG-1IA, AG-1IB, AG-1IC, AG-1, AG-2,
AG-2-2, AG-3, AG-4 and AG-5 (Bolkan and Ribeiro 1985; Sneh et al. 1991; Nelson
et al. 1996).
The aim of the present study was to determine the anastomosis groupings and
pathogenicity of Rhizoctonia isolates obtained from the roots and rhizosphere soils
of bean and soybean that are the main legume crops grown in Samsun province.
Materials and methods
Collection, isolation and identification
Rhizoctonia isolates were obtained from the roots and rhizosphere soils of bean and
soybean plants, showing root rot disease symptoms in Samsun province, Turkey.
Isolations from bean and soybean plants were made from discoloured or necrotic
lesions on root and hypocotyl tissues. Affected tissues were washed under running
tap water, and the surface was disinfected in 1% sodium hypochlorite (NaOCl) for
2–3 minutes and four segments per plant were plated on acidified water agar in a
petri dish (2% water agar amended with 3 ml of 10% lactic acid per litre). Three
replicate isolations were made for each field sample. Immediately after the soil
samples were brought to the laboratory, each composite sample was filled in three
sterile plastic pots and watered to field capacity with sterile water. Three internodal
segments of sterile oat straw about 2–3 cm long were then inserted vertically to each
plastic pot. Pots were covered with plastic sheet to prevent the water loss. After
incubation at room temparature for 3 days, straw segments were removed from the
soil and washed under tap water. They were surface sterilized with 1% NaOCl,
rinsed with sterile distilled water, blotted dry and placed on acidified water agar as in
plant root samples (Ogoshi et al. 1990). After 2 or 3 days incubation at (22 + 2)8C,
hyphal tips were transferred to PDA (Oxoid) for further examination. Isolates were
stored in tubes with oat grains at þ48C.
Rhizoctonia isolates were identified on the basis of characteristics of their
vegetative hyphae; hyphal diameter and nuclear condition (Bandoni 1979), and
hyphal anastomosis with known tester isolates. A modification of the method of
Kronland and Stanghellini (1988) was used to identify AGs. Tester isolates of
R. solani (AG-1, AG-2-1, AG-2-2, AG-3, AG-4, AG-5, AG-6, AG-7, AG-8, AG-9,
AG-10 and AG-11) were provided by Dr. Ogoshi, Hokkaido University, Japan,
Dr. D.E. Carling, University of Alaska Fairbanks, USA and Dr. S.M. Neate, CSIRO,
80
I. Erper et al.
Division of Soils, Australia. Tester isolates of binucleate Rhizoctonia (AG-A, AG-B,
AG-C, AG-D, AG-E, AG-F, AG-G, AG-H, AG-I, AG-K, AG-L, AG-O, AG-P,
AG-Q and AG-S) were provided by Dr. Ogoshi, Hokkaido University, Japan. Tester
isolates of subspecies of W. circinata (W. circinata var. zeae, W. circinata var. oryzae)
were provided by Dr. Hyakumachi, Gifu University, Japan.
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Determination of pathogenicity
Pathogenicity of 21 selected isolates (Table 2) was determined on bean (cv. Lodi) and
soybean (cv. Nova) seedlings. Inoculum was prepared on the moistened sterile oat
grains (with 250 mg/ml chloramphenicol) in tests tubes, which were autoclaved twice
at 24 h intervals, inoculated with plugs of mycelium from cultures grown on PDA
and incubated at 258C for 10 days (Martin 1988).
For seedling tests, plants were grown in plastic pots (1 l) containing sterilized
mixture of sandy loam soil:manure:washed sand (2:2:1,v/v/v), in a greenhouse at
17–258C. Four seeds were sown to a depth of 2 cm in each pot. Plants were
inoculated by placing 5 colonized oat grains in contact with each seedling. In control
treatments, sterile oat grains were used. After 4 weeks from inoculation, plants were
harvested, washed and disease severity ratings were made by using 1–5 scale modified
from Muyolo et al. (1993), where 1, healthy seedling; 2, very little superficial lesions
on roots and hypocothyls; 3, deep and large lesions on the roots or on the
hypocothyl; 4, severe root rot, lesions surrounding hypocothyl, partially restricted
root length and 5, complete root rot. Four replicate pots were used for each
treatment. Disease severity data were subjected to analysis of variance (SPSS version
11.0) and separated using Duncan’s multiple range test (P ¼ 0.05).
Results
Species and AGs of Rhizoctonia isolates
A total of 434 Rhizoctonia isolates belonging to 10 AGs were obtained from roots
and rhizosphere soil of bean and soybean plants in Samsun. Of 296 bean isolates, 205
were obtained from plant root samples and the remaining 91 were from rhizosphere
soil. Number of soybean isolates were less than bean and 60 of the total 138 soybean
isolates were recovered from plant roots and 78 of them were from soil samples.
Among all bean isolates, 59% were R. solani, 32% were binucleate Rhizoctonia and
9% were R. zeae, whereas 36% were R. solani, 49% were binucleate Rhizoctonia and
15% were R. zeae, for those of soybean isolates. Isolates of R. solani obtained from
bean root and rhizosphere soils were distinguished in five AGs: AG-1 (0.6%), AG-4
(85.7%), AG-5 (5.7%), AG-6 (7.4%) and AG-7 (0.6%). Binucleate Rhizoctonia
isolates recovered from bean were grouped in three AGs: AG-A (10.5%), AG-B
(65.2%) and AG-K (24.3%). Isolates of R. solani collected from soybean root and
rhizosphere soils were distinguished in three AGs: AG-4 (61.2%), AG-5 (12.2%) and
AG-6 (26.6%), and isolates of binucleate Rhizoctonia were grouped in three AGs:
AG-A (36.8%), AG-B (57.3%) and AG E (5.9%) (Table 1).
Pathogenicity of the Rhizoctonia isolates
As a result of the pathogenicity test, it was found that the differences among the
virulence of isolates of R. solani, binucleate Rhizoctonia and R. zeae were statistically
81
Archives of Phytopathology and Plant Protection
Table 1. Number of plant and soil isolates of Rhizoctonia spp. and AGs isolated from bean
and soybean in Samsun, Turkey.
Bean
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AGs
Plant isolates
R. solani
AG-1
1
AG-4
110
AG-5
9
AG-6
6
AG-7
–
Binucleate Rhizoctonia
AG-A
3
AG-B
46
AG-E
–
AG-K
21
R. zeae
9
Total
205
Soybean
Soil isolates
Plant isolates
Soil isolates
–
40
1
7
1
–
20
4
10
–
–
10
2
3
–
7
16
–
2
17
91
2
14
2
–
8
60
23
25
2
–
13
78
significant. Virulence differences also existed among the isolates from the same
AG (Table 2). R. solani AG-4 isolates B-141 and S-55 were found to be the most
virulent isolates both on bean and soybean seedlings, whereas S-215 isolate from the
same AG was highly virulent only on bean seedlings. R. solani isolates belonging to
AG-1 (B-25) and AG-6 (B-251 and S-271) were found to be moderately pathogenic
on both plants. AG-7 (B-341) and AG-5 (B-41) were weakly pathogenic on bean
cultivar tested, but same isolates were moderately virulent on soybean. Binucleate
Rhizoctonia AG-B isolates were also moderately pathogenic on bean (B-09) and
soybean (B-160), although the majority of the binucleate Rhizoctonia were weakly
pathogenic on both plants. R. zeae isolates were found to be moderately or weakly
pathogenic on bean and soybean plants.
Discussion
In this study, different AGs of R. solani (AG-1, AG-4, AG-5, AG-6 and AG-7) and
binucleate Rhizoctonia (AG-A, AG-B, AG-E and AG-K) and R. zeae were obtained
from bean and soybean plants and rhizosphere soils in Samsun. In a previous
study carried out in Samsun, AG-2-2, AG-4 and AG-5 were found on bean (Karaca
et al. 2002). However, AG-1, AG-2-1, AG-3, AG-4, AG-5, AG-9, AG-10 and AG-11
of R. solani and AG-A, AG-E, AG-F, AG-G, AG-I and AG-K of binucleate
Rhizoctonia were previously detected on bean in different regions of Turkey (Tuncer
and Erdiller 1990; Demirci and Döken 1995; Eken and Demirci 2004). There is
rather less work on soybean in our country and only AG-4 was obtained from this
plant (Tuncer and Erdiller 1990). In the present study, AG-6 and AG-7 of R. solani
and AG-B of binucleate Rhizoctonia isolated from bean, and AG-5 and AG-6 of
R. solani and AG-A, AG-B and AG-E of binucleate Rhizoctonia isolated from
soybean were reported for the first time in Turkey. R. zeae from bean and soybean
determined in this study was recently reported by the same authors (Erper et al.
2005).
As a result of the pathogenicity tests, it was found that the differences among the
virulence of Rhizoctonia isolates belonging to same or different AGs or species were
82
I. Erper et al.
Table 2.
Pathogenicity of Rhizoctonia species on bean and soybean seedlings.
Disease severitya
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AGs
R. solani
AG-1
AG-4
AG-4
AG-4
AG-4
AG-4
AG-4
AG-5
AG-6
AG-6
AG-7
Binucleate Rhizoctonia
AG-A
AG-B
AG-B
AG-B
AG-B
AG-E
AG-K
R. zeae
Control
Isolate codes
Bean
Soybean
B-25
B-141
S-55
B-18
B-310
S-215
B-95
B-41
B-251
S-271
B-341
2.87; bcdeb
3.75; ab
4.25; a
2.75; cde
3.25; bc
4.12; a
2.50; cde
2.25; de
2.62; cde
2.62; cde
2.00; e
3.12; bcde
4.12; ab
4.87; a
3.75; bc
3.25; bcde
3.75; bc
3.50; bcd
3.25; bcde
2.62; cde
2.75; cde
2.87; cde
B-85
S-97
B-160
S-195
B-09
B-78
B-190
S-215
S-290
B-410
2.62; cde
2.25; de
2.25; de
2.50; cde
3.00; bcd
2.37; cde
2.12; de
2.75; cde
2.62; cde
2.87; bcde
1.12; f
2.37; def
2.75; cde
3.12; bcde
2.75; cde
2.87; cde
2.50; de
2.87; cde
2.37; def
2.25; ef
2.37; def
1.25; f
a
Disease severity was assigned to each plant on a scale of 1–5, in which 1, healthy seedling; 5, complete
root rot.
b
Within columns, means followed by the same letters are not significantly differ from each other according
to the Duncan’s multiple range test (P ¼ 0.05).
statistically significant. It was found that the most virulent isolates were from AG-4
group. Likely, Bolkan and Ribeiro (1985) determined that AG-4 was highly virulent
on soybean hypocotyls, and Phillips (1991) reported that AG-4 isolates caused preemergence death and hypocotyl lesions on bean and soybean plants. In this study,
AG-5 isolate was found to be weakly pathogenic on bean, but caused moderate
symptoms on soybean. Similiarly, Nelson et al. (1996) reported that AG-5 caused
damping off on soybean, but its virulence was rather lower. Also, Ogoshi (1996)
suggested that AG-5 isolates were weakly pathogenic or not pathogenic on plants.
As in AG-5, R. solani isolate belonging to AG-7 was also weakly pathogenic on bean
and moderately pathogenic on soybean, whereas AG-6 was moderately pathogenic
on both plants. AG-7 was thought to be a group with limited pathogenicity, but it was
isolated from soybean plants (Rothrock et al. 1993). AG-6 was reported as agents of
the crater disease of wheat (Carling et al. 1996) and root canker of lucerne (Anderson
et al. 2004), and there was also evidence that it was pathogenic on potato, barley,
lettuce, cauliflower and radish (Carling et al. 1999). In the present study, it was found
that the virulence of R. zeae isolates was lower on soybean, whereas they were
moderately pathogenic on bean. Some R. zeae isolates have been reported as
pathogenic (Leiner and Carling 1994) or weakly pathogenic (Demirci 1998) on
different plants, but it was found to be non pathogenic on soybean (Ploetz et al. 1985).
Archives of Phytopathology and Plant Protection
83
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Binucleate Rhizoctonia AG-B isolate B-09 and B-160 were found to be moderately
pathogenic on bean and soybean, respectively. Other binucleate Rhizoctonia isolates
were weakly pathogenic. Some binucleate Rhizoctonia isolates have been reported as
pathogenic, non-pathogenic or weakly pathogenic on cultivated plants (Sumner 1985;
Yuen et al. 1994). Ploetz et al. (1985) reported that AG-E was pathogenic on young
soybean plants. AG-K was found to be weakly pathogenic on wheat and barley
(Demirci 1998), and it was also previously isolated from bean hypocotyls, but its
virulence was not mentioned (Demirci and Döken 1995).
This group of fungi can cause economic yield losses on plants in Samsun, where
vegetable growing is common. Hence, suitable cultural practices, such as the use of
resistant cultivars and the improvement of soil conditions, will be useful. It is
known that chemical control is not so efficient against soil-borne pathogens like
Rhizoctonia group fungi. Therefore, it will be useful to determine biocontrol agents
that could be effective againts R. solani and to evaluate their efficiency by in vivo and
in vitro trials.
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http://www.informaworld.com/smpp/title~content=t713454295
Identification and pathogenicity of Rhizoctonia species isolated from bean
and soybean plants in Samsun, Turkey
Ismail Erpera; Ibrahim Ozkocb; Gürsel Hatat Karacac
a
Plant Protection Department, Agriculture Faculty, Ondokuz Mayis University, Samsun, Turkey b
Biological Sciences Department, Faculty of Arts and Sciences, Samsun, Turkey c Plant Protection
Department, Agriculture Faculty, Süleyman Demirel University, Isparta, Turkey
Online publication date: 25 January 2011
To cite this Article Erper, Ismail , Ozkoc, Ibrahim and Karaca, Gürsel Hatat(2011) 'Identification and pathogenicity of
Rhizoctonia species isolated from bean and soybean plants in Samsun, Turkey', Archives Of Phytopathology And Plant
Protection, 44: 1, 78 — 84
To link to this Article: DOI: 10.1080/03235400903395427
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Archives of Phytopathology and Plant Protection
Vol. 44, No. 1, January 2011, 78–84
Identification and pathogenicity of Rhizoctonia species isolated from
bean and soybean plants in Samsun, Turkey
Ismail Erpera*, Ibrahim Ozkocb and Gürsel Hatat Karacac
a
Plant Protection Department, Agriculture Faculty, Ondokuz Mayis University, Samsun,
Turkey; bBiological Sciences Department, Faculty of Arts and Sciences, Samsun, Turkey; cPlant
Protection Department, Agriculture Faculty, Süleyman Demirel University, Isparta, Turkey
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(Received 11 September 2009; final version received 24 September 2009)
A total of 434 isolates of Rhizoctonia belonging to 10 anastomosis groups were
obtained from the roots and rhizosphere soils of bean and soybean plants grown in
Samsun, Turkey. AG-4 was found to be the most common group on bean and
soybean plants and AG-5, AG-6, binucleate AG-A, AG-B and R. zeae were other
groups isolated from the both plant species. AG-1, AG-7 and AG-K from bean
and AG-E from soybean were other groups obtained in the study. The
pathogenicity tests on bean and soybean seedlings showed that the highest disease
severities were caused by AG-4 isolates, whereas AG-1 and AG-6 isolates were
moderately pathogenic. Binucleate Rhizoctonia AG-B isolates were also moderately pathogenic, while other binucleate Rhizoctonia were found to be weakly
pathogenic. Rhizoctonia zeae isolates caused moderate disease symptoms on bean,
but soybean plants were slightly affected by this group of isolates. This is the first
reported observation of R. solani AG-6 and AG-7 and binucleate Rhizoctonia AGB on bean, and R. solani AG-5 and AG-6 and binucleate Rhizoctonia AG-A, AG-B
and AG-E on soybean, in Turkey.
Keywords: Rhizoctonia; Phaseolus vulgaris L.; Glycine max L.; anastomosis group;
pathogenicity
Introduction
Bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) are the major legume
crops grown in Samsun, Turkey. Especially, bean is very common in the province,
and with its 105.436 tones production Samsun comes first in our country. Soybean is
the second important legume plant in the province with 11.598 tones production
(Anonymous 2003). Because of the warm and humid weather conditions of the
province, mainly fungal diseases can cause significant yield losses. Among those,
damping off and root rot is very common on legume crops, and Rhizoctonia group
fungi were found to be one of the main agents of the disease (Ecevit et al. 1988).
These fungi are among the soil-borne pathogens, which attacks a wide range
of plants and are distributed all over the world (Ogoshi 1996). R. solani Kühn
[teleomorph: Thanatephorus cucumeris (Frank) Donk.] and binucleate Rhizoctonia
(teleomorph: Ceratobasidium Rogers) are divided into anastomosis groups (AGs)
based on hyphal anastomosis reactions between isolates. R. solani is composed of
*Corresponding author. Email: ismailer@omu.edu.tr
ISSN 0323-5408 print/ISSN 1477-2906 online
Ó 2011 Taylor & Francis
DOI: 10.1080/03235400903395427
http://www.informaworld.com
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Archives of Phytopathology and Plant Protection
79
13 AGs designated as AG-1 to AG-13 (Sneh et al. 1991; Carling et al. 2002;
Woodhall et al. 2007). Only 16 Binucleate Rhizoctonia AGs are currently known
(Sharon et al. 2008). Rhizoctonia zeae and Rhizoctonia oryzae were accepted as
anamorphs of Waitea circinata (Leiner and Carling 1994).
Among Rhizoctonia group fungi, R. solani is the most common and virulent
species and can cause several types of damage, including hypocotyl rot, root rot and
web blight on bean (Galindo et al. 1983; Sumner 1985), and damping-off, root rot,
stem rot, and foliar blight on soybean (Sinclair and Backman 1989). AG-4 is the
major AG worldwide, causing root rot on bean. However, other AGs (AG-1, AG-1IB, AG-2-1, AG-2-2 and AG-5) have also been reported on bean (Muyolo et al.
1993; Echavez-Badel et al. 2000). In Turkey, some R. solani (AG-1, AG 2-1, AG 2-2,
AG-3, AG-4, AG-5, AG-9, AG-10 and AG-11) and binucleate Rhizoctonia AGs
(AG-A, AG-E, AG-F, AG-G, AG-I and AG-K) have previously been recognized
on bean (Demirci and Döken 1995; Karaca et al. 2002; Eken and Demirci 2004).
R. solani AGs reported on soybean were AG-1IA, AG-1IB, AG-1IC, AG-1, AG-2,
AG-2-2, AG-3, AG-4 and AG-5 (Bolkan and Ribeiro 1985; Sneh et al. 1991; Nelson
et al. 1996).
The aim of the present study was to determine the anastomosis groupings and
pathogenicity of Rhizoctonia isolates obtained from the roots and rhizosphere soils
of bean and soybean that are the main legume crops grown in Samsun province.
Materials and methods
Collection, isolation and identification
Rhizoctonia isolates were obtained from the roots and rhizosphere soils of bean and
soybean plants, showing root rot disease symptoms in Samsun province, Turkey.
Isolations from bean and soybean plants were made from discoloured or necrotic
lesions on root and hypocotyl tissues. Affected tissues were washed under running
tap water, and the surface was disinfected in 1% sodium hypochlorite (NaOCl) for
2–3 minutes and four segments per plant were plated on acidified water agar in a
petri dish (2% water agar amended with 3 ml of 10% lactic acid per litre). Three
replicate isolations were made for each field sample. Immediately after the soil
samples were brought to the laboratory, each composite sample was filled in three
sterile plastic pots and watered to field capacity with sterile water. Three internodal
segments of sterile oat straw about 2–3 cm long were then inserted vertically to each
plastic pot. Pots were covered with plastic sheet to prevent the water loss. After
incubation at room temparature for 3 days, straw segments were removed from the
soil and washed under tap water. They were surface sterilized with 1% NaOCl,
rinsed with sterile distilled water, blotted dry and placed on acidified water agar as in
plant root samples (Ogoshi et al. 1990). After 2 or 3 days incubation at (22 + 2)8C,
hyphal tips were transferred to PDA (Oxoid) for further examination. Isolates were
stored in tubes with oat grains at þ48C.
Rhizoctonia isolates were identified on the basis of characteristics of their
vegetative hyphae; hyphal diameter and nuclear condition (Bandoni 1979), and
hyphal anastomosis with known tester isolates. A modification of the method of
Kronland and Stanghellini (1988) was used to identify AGs. Tester isolates of
R. solani (AG-1, AG-2-1, AG-2-2, AG-3, AG-4, AG-5, AG-6, AG-7, AG-8, AG-9,
AG-10 and AG-11) were provided by Dr. Ogoshi, Hokkaido University, Japan,
Dr. D.E. Carling, University of Alaska Fairbanks, USA and Dr. S.M. Neate, CSIRO,
80
I. Erper et al.
Division of Soils, Australia. Tester isolates of binucleate Rhizoctonia (AG-A, AG-B,
AG-C, AG-D, AG-E, AG-F, AG-G, AG-H, AG-I, AG-K, AG-L, AG-O, AG-P,
AG-Q and AG-S) were provided by Dr. Ogoshi, Hokkaido University, Japan. Tester
isolates of subspecies of W. circinata (W. circinata var. zeae, W. circinata var. oryzae)
were provided by Dr. Hyakumachi, Gifu University, Japan.
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Determination of pathogenicity
Pathogenicity of 21 selected isolates (Table 2) was determined on bean (cv. Lodi) and
soybean (cv. Nova) seedlings. Inoculum was prepared on the moistened sterile oat
grains (with 250 mg/ml chloramphenicol) in tests tubes, which were autoclaved twice
at 24 h intervals, inoculated with plugs of mycelium from cultures grown on PDA
and incubated at 258C for 10 days (Martin 1988).
For seedling tests, plants were grown in plastic pots (1 l) containing sterilized
mixture of sandy loam soil:manure:washed sand (2:2:1,v/v/v), in a greenhouse at
17–258C. Four seeds were sown to a depth of 2 cm in each pot. Plants were
inoculated by placing 5 colonized oat grains in contact with each seedling. In control
treatments, sterile oat grains were used. After 4 weeks from inoculation, plants were
harvested, washed and disease severity ratings were made by using 1–5 scale modified
from Muyolo et al. (1993), where 1, healthy seedling; 2, very little superficial lesions
on roots and hypocothyls; 3, deep and large lesions on the roots or on the
hypocothyl; 4, severe root rot, lesions surrounding hypocothyl, partially restricted
root length and 5, complete root rot. Four replicate pots were used for each
treatment. Disease severity data were subjected to analysis of variance (SPSS version
11.0) and separated using Duncan’s multiple range test (P ¼ 0.05).
Results
Species and AGs of Rhizoctonia isolates
A total of 434 Rhizoctonia isolates belonging to 10 AGs were obtained from roots
and rhizosphere soil of bean and soybean plants in Samsun. Of 296 bean isolates, 205
were obtained from plant root samples and the remaining 91 were from rhizosphere
soil. Number of soybean isolates were less than bean and 60 of the total 138 soybean
isolates were recovered from plant roots and 78 of them were from soil samples.
Among all bean isolates, 59% were R. solani, 32% were binucleate Rhizoctonia and
9% were R. zeae, whereas 36% were R. solani, 49% were binucleate Rhizoctonia and
15% were R. zeae, for those of soybean isolates. Isolates of R. solani obtained from
bean root and rhizosphere soils were distinguished in five AGs: AG-1 (0.6%), AG-4
(85.7%), AG-5 (5.7%), AG-6 (7.4%) and AG-7 (0.6%). Binucleate Rhizoctonia
isolates recovered from bean were grouped in three AGs: AG-A (10.5%), AG-B
(65.2%) and AG-K (24.3%). Isolates of R. solani collected from soybean root and
rhizosphere soils were distinguished in three AGs: AG-4 (61.2%), AG-5 (12.2%) and
AG-6 (26.6%), and isolates of binucleate Rhizoctonia were grouped in three AGs:
AG-A (36.8%), AG-B (57.3%) and AG E (5.9%) (Table 1).
Pathogenicity of the Rhizoctonia isolates
As a result of the pathogenicity test, it was found that the differences among the
virulence of isolates of R. solani, binucleate Rhizoctonia and R. zeae were statistically
81
Archives of Phytopathology and Plant Protection
Table 1. Number of plant and soil isolates of Rhizoctonia spp. and AGs isolated from bean
and soybean in Samsun, Turkey.
Bean
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AGs
Plant isolates
R. solani
AG-1
1
AG-4
110
AG-5
9
AG-6
6
AG-7
–
Binucleate Rhizoctonia
AG-A
3
AG-B
46
AG-E
–
AG-K
21
R. zeae
9
Total
205
Soybean
Soil isolates
Plant isolates
Soil isolates
–
40
1
7
1
–
20
4
10
–
–
10
2
3
–
7
16
–
2
17
91
2
14
2
–
8
60
23
25
2
–
13
78
significant. Virulence differences also existed among the isolates from the same
AG (Table 2). R. solani AG-4 isolates B-141 and S-55 were found to be the most
virulent isolates both on bean and soybean seedlings, whereas S-215 isolate from the
same AG was highly virulent only on bean seedlings. R. solani isolates belonging to
AG-1 (B-25) and AG-6 (B-251 and S-271) were found to be moderately pathogenic
on both plants. AG-7 (B-341) and AG-5 (B-41) were weakly pathogenic on bean
cultivar tested, but same isolates were moderately virulent on soybean. Binucleate
Rhizoctonia AG-B isolates were also moderately pathogenic on bean (B-09) and
soybean (B-160), although the majority of the binucleate Rhizoctonia were weakly
pathogenic on both plants. R. zeae isolates were found to be moderately or weakly
pathogenic on bean and soybean plants.
Discussion
In this study, different AGs of R. solani (AG-1, AG-4, AG-5, AG-6 and AG-7) and
binucleate Rhizoctonia (AG-A, AG-B, AG-E and AG-K) and R. zeae were obtained
from bean and soybean plants and rhizosphere soils in Samsun. In a previous
study carried out in Samsun, AG-2-2, AG-4 and AG-5 were found on bean (Karaca
et al. 2002). However, AG-1, AG-2-1, AG-3, AG-4, AG-5, AG-9, AG-10 and AG-11
of R. solani and AG-A, AG-E, AG-F, AG-G, AG-I and AG-K of binucleate
Rhizoctonia were previously detected on bean in different regions of Turkey (Tuncer
and Erdiller 1990; Demirci and Döken 1995; Eken and Demirci 2004). There is
rather less work on soybean in our country and only AG-4 was obtained from this
plant (Tuncer and Erdiller 1990). In the present study, AG-6 and AG-7 of R. solani
and AG-B of binucleate Rhizoctonia isolated from bean, and AG-5 and AG-6 of
R. solani and AG-A, AG-B and AG-E of binucleate Rhizoctonia isolated from
soybean were reported for the first time in Turkey. R. zeae from bean and soybean
determined in this study was recently reported by the same authors (Erper et al.
2005).
As a result of the pathogenicity tests, it was found that the differences among the
virulence of Rhizoctonia isolates belonging to same or different AGs or species were
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I. Erper et al.
Table 2.
Pathogenicity of Rhizoctonia species on bean and soybean seedlings.
Disease severitya
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AGs
R. solani
AG-1
AG-4
AG-4
AG-4
AG-4
AG-4
AG-4
AG-5
AG-6
AG-6
AG-7
Binucleate Rhizoctonia
AG-A
AG-B
AG-B
AG-B
AG-B
AG-E
AG-K
R. zeae
Control
Isolate codes
Bean
Soybean
B-25
B-141
S-55
B-18
B-310
S-215
B-95
B-41
B-251
S-271
B-341
2.87; bcdeb
3.75; ab
4.25; a
2.75; cde
3.25; bc
4.12; a
2.50; cde
2.25; de
2.62; cde
2.62; cde
2.00; e
3.12; bcde
4.12; ab
4.87; a
3.75; bc
3.25; bcde
3.75; bc
3.50; bcd
3.25; bcde
2.62; cde
2.75; cde
2.87; cde
B-85
S-97
B-160
S-195
B-09
B-78
B-190
S-215
S-290
B-410
2.62; cde
2.25; de
2.25; de
2.50; cde
3.00; bcd
2.37; cde
2.12; de
2.75; cde
2.62; cde
2.87; bcde
1.12; f
2.37; def
2.75; cde
3.12; bcde
2.75; cde
2.87; cde
2.50; de
2.87; cde
2.37; def
2.25; ef
2.37; def
1.25; f
a
Disease severity was assigned to each plant on a scale of 1–5, in which 1, healthy seedling; 5, complete
root rot.
b
Within columns, means followed by the same letters are not significantly differ from each other according
to the Duncan’s multiple range test (P ¼ 0.05).
statistically significant. It was found that the most virulent isolates were from AG-4
group. Likely, Bolkan and Ribeiro (1985) determined that AG-4 was highly virulent
on soybean hypocotyls, and Phillips (1991) reported that AG-4 isolates caused preemergence death and hypocotyl lesions on bean and soybean plants. In this study,
AG-5 isolate was found to be weakly pathogenic on bean, but caused moderate
symptoms on soybean. Similiarly, Nelson et al. (1996) reported that AG-5 caused
damping off on soybean, but its virulence was rather lower. Also, Ogoshi (1996)
suggested that AG-5 isolates were weakly pathogenic or not pathogenic on plants.
As in AG-5, R. solani isolate belonging to AG-7 was also weakly pathogenic on bean
and moderately pathogenic on soybean, whereas AG-6 was moderately pathogenic
on both plants. AG-7 was thought to be a group with limited pathogenicity, but it was
isolated from soybean plants (Rothrock et al. 1993). AG-6 was reported as agents of
the crater disease of wheat (Carling et al. 1996) and root canker of lucerne (Anderson
et al. 2004), and there was also evidence that it was pathogenic on potato, barley,
lettuce, cauliflower and radish (Carling et al. 1999). In the present study, it was found
that the virulence of R. zeae isolates was lower on soybean, whereas they were
moderately pathogenic on bean. Some R. zeae isolates have been reported as
pathogenic (Leiner and Carling 1994) or weakly pathogenic (Demirci 1998) on
different plants, but it was found to be non pathogenic on soybean (Ploetz et al. 1985).
Archives of Phytopathology and Plant Protection
83
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Binucleate Rhizoctonia AG-B isolate B-09 and B-160 were found to be moderately
pathogenic on bean and soybean, respectively. Other binucleate Rhizoctonia isolates
were weakly pathogenic. Some binucleate Rhizoctonia isolates have been reported as
pathogenic, non-pathogenic or weakly pathogenic on cultivated plants (Sumner 1985;
Yuen et al. 1994). Ploetz et al. (1985) reported that AG-E was pathogenic on young
soybean plants. AG-K was found to be weakly pathogenic on wheat and barley
(Demirci 1998), and it was also previously isolated from bean hypocotyls, but its
virulence was not mentioned (Demirci and Döken 1995).
This group of fungi can cause economic yield losses on plants in Samsun, where
vegetable growing is common. Hence, suitable cultural practices, such as the use of
resistant cultivars and the improvement of soil conditions, will be useful. It is
known that chemical control is not so efficient against soil-borne pathogens like
Rhizoctonia group fungi. Therefore, it will be useful to determine biocontrol agents
that could be effective againts R. solani and to evaluate their efficiency by in vivo and
in vitro trials.
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