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Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all
Myea/. Res. 93 (2): 156--160 (1989)
156
Printed in Great Britai"
Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all
M. M. DEWAN AND K. SIV ASITHAMP ARAM Soil Science and PlaYll Nulrition Group, School of Agriculture, The University of Weslern Auslralia, Nedlands 6009, Auslralia
Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all. Mycological Research 93 (2): 156-160 (1939). Two temperatures (15 and 20°C) and two levels of soil water potential (- 0·0015 MPa and - 0·001 MPa) were used to test the ability of a sterile red fungus (SRF) to protect wheat (Trilicium aeslivum cv. Gamenya) and rye-grass (Lolium rigidum cv. Wimmera) from infection by the take-all fungus (Gaeumannomyces graminis var. Iritiei (Ggt)). The SRF protected wheat and rye-grass plants from infection by Ggt at both levels of soil moisture and temperature. The SRF promoted the growth of wheat and rye-grass in both the SRF alone and SRF + Ggt treatments at - 0·0015 MPa and -0'001 MPa, and 15 and 20°. Shoot and root weights were greatest at -0·001 MPa and 15° for wheat, and -0·001 MPa and 20° for rye-grass, in all treatments. At both temperatures the percentage of dead plants of wheat or rye-grass was greater at - 0·0015 MPa than at - 0·001 MPa in the Ggt-alone treatment. The reduction of shoot and root weights of wheat and rye-grass by the take-all fungus was most severe at - 0'0015 MPa and 20°. The SRF promoted the growth of the barley (Hordeum vulgare cv. Stirling), great brome (Bromus diandrus), chick pea (eieer arientinum cv. Opal), lupins (Lupinus angustifolius cv. Yandeej, medic (Medicago polymorpha L. cv. Santiago), oats (Avena sativa cv. Swan), peas (Pisum salivum cv. Dundale), rape (Brassica napus cv. Wesbrook), rye-grass (Lolium rigidum cv. Wimmera) and subterranean clover (Trifolium sublerraneum cv. Nungarin) which are used as rotation crops with the wheat. Although the roots of all these plants were found to be infected and covered by the SRF, the recovery of the SRF was more frequent from the roots of wheat, rye-grass, oats, barley and great brome than peas, lupins, medic, subterranean clover and chick pea. Key words: Gaeumannomyces graminis var. Iritici, Soil water potential, Soil temperature, Triticum, Growth promotion.
Sterile fungi are common in roots of wheat and rye-grass (Peterson, 1958; Waid, 1957, 1974; Sivasithamparam. 1977; Hall, 1987). A sterile red fungus (SRF) isolated from wheat (Triticium aestivum L.) and rye-grass (Lolium rigidum L.) in Western Australia was found to promote the growth of wheat and rye-grass and also afford protection for them from takeall (Dewan & Sivasithamparam, 1988. 1989). As the studies conducted already on this fungus indicate that it has great potential as a biocontrol agent for take-all in the Western Australian grain belt, it is necessary to know what effect it may have on crops planted in rotation with wheat and how its effect on wheat and take-all may be affected by the soil temperature and moisture regimes which prevail in the grain belt at seedling stages of crop growth. The aim of this study was to investigate the effect of temperature and soil moisture on the amount of protection from take-all provided to wheat and rye-grass by the SRF. The pathogenicity of the SRF on crop species grown in rotation with wheat was also examined.
MATERIALS AND METHODS Soil moisture and temperature Soil from Lancelin. Western Australia. a brown sand (Dewan & Sivasithamparam, 1989). was used.
For the preparation of inocula. rye-grass seeds were washed and autoclaved at 120°C for 50 min in 40 g lots within 250 ml flasks. Each flask of rye-grass seeds was then inoculated with five discs (5 mm diam) of agar with growing margins of the SRF or Gaeumannomyces graminis v. Arx & Olivier var. trifid Walker (Ggt) isolates cultured on PDA. The inoculated seeds were incubated at 20 ± 2° for 10 d. The inoculum (20 g) of each fungus was mixed with 4 kg sterilized soil (0'5 % w /w). This soil had been sterilized by autoclaving at 120° for 50 min on three consecutive days. Soil (400 g) with inoculum of each fungus was put into each of 10 replicate cups (10'5 x 7 em). For each treatment, five of these cups were planted with 10 seeds in each of wheat, and the other five planted with 10 seeds of rye-grass. The soil within cups was maintained at - 0'0015 or - 0'001 MPa water potential and placed in an illuminated growth chamber maintaining either
M. M. Dewan and K. Sivasithamparam
157
Fig. 1.(A and B) Percentage of plants of wheat and ryegrass killed by Gaeumarrrromyces gramirris var. trifici (Ggt) at 150 (A) and 20 0 (B), and -0-0015 MPa or -0'001 MPa. The treatments were: -0'0015 MPa+Ggt (wheat) = 6-6, -0'001 MPa+Ggt (wheat) = f::,---f::" -0'0015 MPa+Ggt (rye-grass) = ....- ...., -0-001 MPa+Ggt (rye-grass) = .... --- ...., -0'0015 MPa+Ggt and sterile red fungus (SRF) (wheat) = 0-0, -0'001 MPa+Ggt and SRF (wheat) = 0---0, -0'0015 MPa+Ggt and SRF (rye-grass) = . - . and -0'001 MPa+Ggt and SRF (rye-grass) = .--- • . Bars show L.S.D., P < 0'05.
100
100
A
90
70
~
"'" c s:'"
80 70
f::,
/
60
"0 "0
90
I
80
50
/
Vl
40
60
6-
50
6-
40
/// Iii
li
30
30
/'" .....
,//
20
~I ~
10 ..., ~--
0
- ...... ..........
10
~-~
0
-A
--
14 Time (days)
7
20
...................
..,," "" -.......
B
21
14 Time (days)
7
28
21
28
Table 1. Effect of inoculation with sterile red fungus (SRF), SRF + Gaeumarrrromyces gramirris var. frifici (Ggt) and Ggt alone on fresh shoot and root weights (g) of wheat and rye-grass at two levels of soil water potential (-0'0015 MPa and -0'001 MPa) and temperature (15 and 20 0) -0'001 MPa
-0'0015 MPa
Shoot wt
Root wt
Shoot wt
Root wt
1'20
1'08
0'44
2'04 0'48
2'76
0'40
0'54
1'44 0'60
0'72
1'92 0'60
2'36 0'60
3'12
0'48
0'66
2'16 0'68
2'92 0'84
2'04 0-48
1'32 0-52
1'96 0'68
2'26 0-48
2'98 0'60
2'24 0-74
3'00 0-92
0'64
0'84
0'28
0'44
0'12
0'10
0'08
1'12 0'15
1'20 0'20
0'60 0'20
0'64
0'14
Shoot wt
Control Wheat Rye-grass
1'60
2'06
0'28
0'40
SRF Wheat Rye-grass
1'76 0'48
2'36
1'48
0'48
SRF+Ggt Wheat Rye-grass
1'68 0'36
L.S.D.,
20 0
Root wt
Treatment
Ggt-alone Wheat Rye-grass
ISO
20 0
150
Root wt
Shoot wt
P> 0-05 for shoot and root weights of wheat
=
0'27, rye-grass
=
0'08.
2'20
0'20
158
Effect of a sterile fungus on rotation crops and take-all
± 1 for 4 wk. The dead plants of wheat and ryegrass were washed free of soil and assessed for shoot and root weights and root damage. The root-rot was rated on a scale where the 1 indicated > 0-10 % of roots rotted; 2 = > 15 or 20 0
10-30%; 3 = > 30-50%; 90%; 6 = > 90-100%.
4
= >
50-70%;
5
= >
70-
Host range
The preparation and rate of inoculum of SRF (0' 5 % w /w) used for the host range experiment in non-sterilized Lancelin soil were the same as in the preceding experiment. Five cups were planted with 10 seeds in each of barley (Hordeum vlugare L. cv. Stirling), great brome (Bromus diandrus L.), medic (Medicago polymorpha L. cv. Santiago), oats (Avena sativa L. cv. Swan), rape (Brassica napus L. cv. Wesbrook), rye-grass (Lolium
rigidum L. cv. Wimmera), subterranean clover (Trifolium subterraneum L. cv. Nungarin) and wheat (Triticum aestivum L. cv. Gamenya), or five seeds in each of chick pea (Cicer arientinum L. cv. Opal), lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisum sativum L. cv. Dundale). Soil was maintained at - 0'0013 MPa. After 4 wk at 15 ± 2 0 in an illuminated growth chamber, the roots were washed free of soil and plants were assessed for shoot and root weights. To assess percentage of roots colonized by the SRF, the roots of each plant were cut into small pieces (ca 0'5-1 em). Random samples (100 segments from each plant) of root pieces were plated on potato dextrose agar (PDA) and the recovery of SRF from root pieces counted after incubation for 24 h at 20 0 .
Fig. 2. Root-rot rating of wheat and rye-grass infected by Gael-/mannomyces graminis var. trifici and/or sterile red fungus (SRF) at -0'0015 MPa and 15° (.), -0'0015 MPa and 20° (0), -0'001 MPa and 15° (0) and -0'001 MPa and 20 0 (~). Bar shows P
<
loS.D.,
0'05. 6
I
5 4 01J
.:
~ 3
~
15 2 0
: :
0::
:::::
o
SRF + Ggt
SRF
Ggt alone
Table 2. Fresh shoot and root weight (g) of plants commonly grown in rotation with wheat in non-sterile soil infested with the sterile red fungus (SRF). Control soil received no added fungi Shoot wt'
Barley Brame-grass Chick pea Lupins Medic Oats Peas Rape Rye-grass Subterranean clover Wheat
Root wt'
Control
SRF
Control
SRF
loS. D.,
1'92 0'48 8'28 6'76 0'54
2'32 0'72 10'72 7'26 0'88 1'88 8'60 0'9 0'45 1'26 2'42
2'20 0'78 10'82 6'80 0'52 2'90 11'82 0'44 0.32 1'08 2'30
2'68 1'16 11'96 7'20 0'76 3'40 12'12 0'74 0'46 1'56 3'10
0'10 0'12 0'69 0'30 0'10 0'20 0'45 0'08 0'06 0'14 0'18
2'46 7'90 0'66 0'34 0'98 1'94
P < 0'05
'Shoot and root weights of chickpea, lupins and peas are means of 5 plants from each replicate pot, while other treatments show means fram 10 plants in each pot.
M. M. Dewan and K. Sivasithamparam
159
Fig. 3. Roots of wheat with (A) and without (B) colorization by the sterile red fungus, 3 wk after planting.
(A)
RESULTS
Soil moisture and temperature The SRF protected wheat and rye-grass from infection by the take-all fungus at both levels of soil water potential (- 0'0015 and - 0'001 MPa) and temperature (15 and 20°) (Fig. 1 A, B). In Ggt-alone treatments, the percentage of dead plants of wheat and rye-grass was greater at - 0'0015 MPa than at - 0'001 MPa. The isolate of Ggt was more pathogenic on wheat than on rye-grass. The SRF promoted growth of wheat and rye-grass in the SRF alone and SRF + Ggt treatments at - 0'0015 and - 0'001 MPa and at 15 and 20°, but promotion over controls was greatest at - 0'001 MPa and 15° for wheat. and at - 0'001 MPa and 20° for rye-grass. The reductions of shoot and root weights of wheat and ryegrass caused by the take-all fungus were most severe at - 0'0015 MPa and 20° (Table 1). Under all conditions, the roots of wheat and rye-grass were extensively rotted in Ggt-alone treatments, but the greatest damage on wheat and rye-grass occurred at - 0'0015 MPa and 20° (Fig. 2). The SRF caused no damage to the roots of wheat or rye-grass in SRF-alone treatment. while some symptoms of take-all disease was evident on the roots of wheat in SRF + Ggt treatment at - 0'0015 MPa and 15 or 20°. This effect. however, was not reflected in the shoot and root weights.
(B)
extent of colonization. The recovery of the SRF was more frequent from the roots of wheat. rye-grass, oats, barley and great brome than peas, lupins, medic, subterranean clover and chick pea (Fig. 4).
Fig. 4. Percentage of root pieces of barley (B), great brome (G.B.), chickpea (C), subterranean dover (S.c.), lupins (L). medic (M), oats (0), peas (P), rape (R), rye-grass (R.G.) and wheat (W) yielding sterile red fungus (SRF) after being planted in soil infested with SRF for 4 wk. Bar shows L.S.v.. P < 0'05.
Host range The SRF increased the shoot and root fresh weights of barley, great brome, chick pea, lupins, medic, oats, peas, rape, ryegrass, subterranean clover and wheat (Table 2). Although the roots of all these plants were found to be infected and covered by the SRF (Fig. 3), some differences were evident in the
B G.B. C S.c. L
MOP
R R.G. W
Effect of a sterile fungus on rotation crops and take-all Growth promotion by the SRF on these hosts was very pronounced three weeks after planting.
160 Glenn for advice on water relations. One of us (M. M. D.) was supported by a generous grant from the Ministry of Higher Education, Government of Iraq.
DISCUSSION The SRF appeared to be active at both levels of soil moisture and temperature. These were chosen to match those that prevail in the Western Australian grain belt at the beginning of the cropping season (May/June). As these soil conditions are equally suitable for the activity of the SRF as they are for the take-all fungus (Sivasithamparam & Parker, 1981), the SRF should compete effectively with the take-all fungus in and around the wheat roots in the field if all other conditions are favourable. In several aspects the suitability of SRF as a biocontrol agent resembles that of Laetisaria arvahs Burdsall, which also was originally isolated as a sterile fungus (Burdsall et al., 1980). Hoch & Abawi (1979) found that L. arvahs was active over the range of temperatures and moistures that favour the high incidence of. and damage caused by, Pythium disease. They found that L. arvahs was non-pathegenic to a range of crop plants commonly grown in rotation with beet and that it was also easy to produce large amounts of inoculum for use against plant pathogens. Another attractive feature about the SRF is that in addition to its ability to produce antibiotics (Dewan & Sivasithamparam, 1989), it colonizes the root cortex rapidly (Dewan & Sivasithamparam, unpub!.), unlike Trichoderma spp. which appear to preferentially colonize soil and commonly inhabit soils having high moisture content (Baker & Cook, 1974). This study also showed that the roots of graminaceous plants were covered more rapidly and extensively by the mycelia of the SRF than those of other crops. Although the SRF appears to show preference for the roots of certain plants it was non-pathogenic to all those tested, indicating that if used as an inoculant of wheat it is unlikely to cause damage to any of the crops which are grown in rotation with wheat in Western Australia. We wish to thank Mr A. Ali, Mr T. Armitage, Mr H. Saoub, Mr M. Munasley for their valuable assistance and Mrs O. (Received for publication 17 May 1988)
REFERENCES BAKER, K. F. & COOK, R. j. (1974). Biological Control of Plant Pathogens. W. H. Freeman, San Francisco. American Phytopathological Society, St Paul, MN. BURDSALL, H. H., HOCH, H. c.. BOOSALIS, M. G. & SETLIFF, E. C. (1980). Laetisaria arvalis (Aphyllophorales, Corticiaceae): a possible biological control agent for Rhizocionia solani and Pythium species. Mycologia 72, 728-736. DEWAN, M. M. & SIVASITHAMPARAM, K. (1988). A plant growth promoting sterile fungus from wheat and rye-grass roots with a potential for suppressing take-all. Transactions of the British Mycological Society 91, 687-692.
DEWAN, M. M. & SIVASITHAMPARAM, K. (1989). Behaviour of a plant growth promoting sterile fungus on agar and roots of ryegrass and wheat. Mycological Research 93, 161-166. HALL, G. (1987). SEM studies of sterile fungi on roots of sterile wheat seedlings. Transactions of the British Mycological Society 88, 549-553.
HOCH, H. C. & ABAWI, G. S. (1979). Biological control of Pythium root rot of table beets with Corticium sp. Phytopathology 69, 417-419.
PETERSON, E. A. (1958). Observations on fungi associated with plant roots. Canadian Journal of Microbiology 4, 257-265. SIVASITHAMPARAM, K. (1977). Wheat rhizosphere and effect of selected micro-organisms on the take-all fungus. PhD. Thesis, The University of Western Australia. SIVASITHAMPARAM, K. & PARKER, C. A. (1981). Physiology and Nutrition in Culture. In Biology and Control of Take-All (ed. M. j. C. Asher & P. j. Shipton), pp. 125-150. London and New York: Academic Press. WAlD, j. S. (1957). Distribution of fungi within the decomposing tissue of rye-grass roots. Transactions of the British Mycological Society 40, 391-406.
WAlD, j. S. (1974). The decomposition of roots. In The Biology of Plant Litter Decomposition 1 (ed. C. H. Dickinson & G. j. F. Pugh), pp. 175-210. London: Academic Press.
156
Printed in Great Britai"
Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all
M. M. DEWAN AND K. SIV ASITHAMP ARAM Soil Science and PlaYll Nulrition Group, School of Agriculture, The University of Weslern Auslralia, Nedlands 6009, Auslralia
Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all. Mycological Research 93 (2): 156-160 (1939). Two temperatures (15 and 20°C) and two levels of soil water potential (- 0·0015 MPa and - 0·001 MPa) were used to test the ability of a sterile red fungus (SRF) to protect wheat (Trilicium aeslivum cv. Gamenya) and rye-grass (Lolium rigidum cv. Wimmera) from infection by the take-all fungus (Gaeumannomyces graminis var. Iritiei (Ggt)). The SRF protected wheat and rye-grass plants from infection by Ggt at both levels of soil moisture and temperature. The SRF promoted the growth of wheat and rye-grass in both the SRF alone and SRF + Ggt treatments at - 0·0015 MPa and -0'001 MPa, and 15 and 20°. Shoot and root weights were greatest at -0·001 MPa and 15° for wheat, and -0·001 MPa and 20° for rye-grass, in all treatments. At both temperatures the percentage of dead plants of wheat or rye-grass was greater at - 0·0015 MPa than at - 0·001 MPa in the Ggt-alone treatment. The reduction of shoot and root weights of wheat and rye-grass by the take-all fungus was most severe at - 0'0015 MPa and 20°. The SRF promoted the growth of the barley (Hordeum vulgare cv. Stirling), great brome (Bromus diandrus), chick pea (eieer arientinum cv. Opal), lupins (Lupinus angustifolius cv. Yandeej, medic (Medicago polymorpha L. cv. Santiago), oats (Avena sativa cv. Swan), peas (Pisum salivum cv. Dundale), rape (Brassica napus cv. Wesbrook), rye-grass (Lolium rigidum cv. Wimmera) and subterranean clover (Trifolium sublerraneum cv. Nungarin) which are used as rotation crops with the wheat. Although the roots of all these plants were found to be infected and covered by the SRF, the recovery of the SRF was more frequent from the roots of wheat, rye-grass, oats, barley and great brome than peas, lupins, medic, subterranean clover and chick pea. Key words: Gaeumannomyces graminis var. Iritici, Soil water potential, Soil temperature, Triticum, Growth promotion.
Sterile fungi are common in roots of wheat and rye-grass (Peterson, 1958; Waid, 1957, 1974; Sivasithamparam. 1977; Hall, 1987). A sterile red fungus (SRF) isolated from wheat (Triticium aestivum L.) and rye-grass (Lolium rigidum L.) in Western Australia was found to promote the growth of wheat and rye-grass and also afford protection for them from takeall (Dewan & Sivasithamparam, 1988. 1989). As the studies conducted already on this fungus indicate that it has great potential as a biocontrol agent for take-all in the Western Australian grain belt, it is necessary to know what effect it may have on crops planted in rotation with wheat and how its effect on wheat and take-all may be affected by the soil temperature and moisture regimes which prevail in the grain belt at seedling stages of crop growth. The aim of this study was to investigate the effect of temperature and soil moisture on the amount of protection from take-all provided to wheat and rye-grass by the SRF. The pathogenicity of the SRF on crop species grown in rotation with wheat was also examined.
MATERIALS AND METHODS Soil moisture and temperature Soil from Lancelin. Western Australia. a brown sand (Dewan & Sivasithamparam, 1989). was used.
For the preparation of inocula. rye-grass seeds were washed and autoclaved at 120°C for 50 min in 40 g lots within 250 ml flasks. Each flask of rye-grass seeds was then inoculated with five discs (5 mm diam) of agar with growing margins of the SRF or Gaeumannomyces graminis v. Arx & Olivier var. trifid Walker (Ggt) isolates cultured on PDA. The inoculated seeds were incubated at 20 ± 2° for 10 d. The inoculum (20 g) of each fungus was mixed with 4 kg sterilized soil (0'5 % w /w). This soil had been sterilized by autoclaving at 120° for 50 min on three consecutive days. Soil (400 g) with inoculum of each fungus was put into each of 10 replicate cups (10'5 x 7 em). For each treatment, five of these cups were planted with 10 seeds in each of wheat, and the other five planted with 10 seeds of rye-grass. The soil within cups was maintained at - 0'0015 or - 0'001 MPa water potential and placed in an illuminated growth chamber maintaining either
M. M. Dewan and K. Sivasithamparam
157
Fig. 1.(A and B) Percentage of plants of wheat and ryegrass killed by Gaeumarrrromyces gramirris var. trifici (Ggt) at 150 (A) and 20 0 (B), and -0-0015 MPa or -0'001 MPa. The treatments were: -0'0015 MPa+Ggt (wheat) = 6-6, -0'001 MPa+Ggt (wheat) = f::,---f::" -0'0015 MPa+Ggt (rye-grass) = ....- ...., -0-001 MPa+Ggt (rye-grass) = .... --- ...., -0'0015 MPa+Ggt and sterile red fungus (SRF) (wheat) = 0-0, -0'001 MPa+Ggt and SRF (wheat) = 0---0, -0'0015 MPa+Ggt and SRF (rye-grass) = . - . and -0'001 MPa+Ggt and SRF (rye-grass) = .--- • . Bars show L.S.D., P < 0'05.
100
100
A
90
70
~
"'" c s:'"
80 70
f::,
/
60
"0 "0
90
I
80
50
/
Vl
40
60
6-
50
6-
40
/// Iii
li
30
30
/'" .....
,//
20
~I ~
10 ..., ~--
0
- ...... ..........
10
~-~
0
-A
--
14 Time (days)
7
20
...................
..,," "" -.......
B
21
14 Time (days)
7
28
21
28
Table 1. Effect of inoculation with sterile red fungus (SRF), SRF + Gaeumarrrromyces gramirris var. frifici (Ggt) and Ggt alone on fresh shoot and root weights (g) of wheat and rye-grass at two levels of soil water potential (-0'0015 MPa and -0'001 MPa) and temperature (15 and 20 0) -0'001 MPa
-0'0015 MPa
Shoot wt
Root wt
Shoot wt
Root wt
1'20
1'08
0'44
2'04 0'48
2'76
0'40
0'54
1'44 0'60
0'72
1'92 0'60
2'36 0'60
3'12
0'48
0'66
2'16 0'68
2'92 0'84
2'04 0-48
1'32 0-52
1'96 0'68
2'26 0-48
2'98 0'60
2'24 0-74
3'00 0-92
0'64
0'84
0'28
0'44
0'12
0'10
0'08
1'12 0'15
1'20 0'20
0'60 0'20
0'64
0'14
Shoot wt
Control Wheat Rye-grass
1'60
2'06
0'28
0'40
SRF Wheat Rye-grass
1'76 0'48
2'36
1'48
0'48
SRF+Ggt Wheat Rye-grass
1'68 0'36
L.S.D.,
20 0
Root wt
Treatment
Ggt-alone Wheat Rye-grass
ISO
20 0
150
Root wt
Shoot wt
P> 0-05 for shoot and root weights of wheat
=
0'27, rye-grass
=
0'08.
2'20
0'20
158
Effect of a sterile fungus on rotation crops and take-all
± 1 for 4 wk. The dead plants of wheat and ryegrass were washed free of soil and assessed for shoot and root weights and root damage. The root-rot was rated on a scale where the 1 indicated > 0-10 % of roots rotted; 2 = > 15 or 20 0
10-30%; 3 = > 30-50%; 90%; 6 = > 90-100%.
4
= >
50-70%;
5
= >
70-
Host range
The preparation and rate of inoculum of SRF (0' 5 % w /w) used for the host range experiment in non-sterilized Lancelin soil were the same as in the preceding experiment. Five cups were planted with 10 seeds in each of barley (Hordeum vlugare L. cv. Stirling), great brome (Bromus diandrus L.), medic (Medicago polymorpha L. cv. Santiago), oats (Avena sativa L. cv. Swan), rape (Brassica napus L. cv. Wesbrook), rye-grass (Lolium
rigidum L. cv. Wimmera), subterranean clover (Trifolium subterraneum L. cv. Nungarin) and wheat (Triticum aestivum L. cv. Gamenya), or five seeds in each of chick pea (Cicer arientinum L. cv. Opal), lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisum sativum L. cv. Dundale). Soil was maintained at - 0'0013 MPa. After 4 wk at 15 ± 2 0 in an illuminated growth chamber, the roots were washed free of soil and plants were assessed for shoot and root weights. To assess percentage of roots colonized by the SRF, the roots of each plant were cut into small pieces (ca 0'5-1 em). Random samples (100 segments from each plant) of root pieces were plated on potato dextrose agar (PDA) and the recovery of SRF from root pieces counted after incubation for 24 h at 20 0 .
Fig. 2. Root-rot rating of wheat and rye-grass infected by Gael-/mannomyces graminis var. trifici and/or sterile red fungus (SRF) at -0'0015 MPa and 15° (.), -0'0015 MPa and 20° (0), -0'001 MPa and 15° (0) and -0'001 MPa and 20 0 (~). Bar shows P
<
loS.D.,
0'05. 6
I
5 4 01J
.:
~ 3
~
15 2 0
: :
0::
:::::
o
SRF + Ggt
SRF
Ggt alone
Table 2. Fresh shoot and root weight (g) of plants commonly grown in rotation with wheat in non-sterile soil infested with the sterile red fungus (SRF). Control soil received no added fungi Shoot wt'
Barley Brame-grass Chick pea Lupins Medic Oats Peas Rape Rye-grass Subterranean clover Wheat
Root wt'
Control
SRF
Control
SRF
loS. D.,
1'92 0'48 8'28 6'76 0'54
2'32 0'72 10'72 7'26 0'88 1'88 8'60 0'9 0'45 1'26 2'42
2'20 0'78 10'82 6'80 0'52 2'90 11'82 0'44 0.32 1'08 2'30
2'68 1'16 11'96 7'20 0'76 3'40 12'12 0'74 0'46 1'56 3'10
0'10 0'12 0'69 0'30 0'10 0'20 0'45 0'08 0'06 0'14 0'18
2'46 7'90 0'66 0'34 0'98 1'94
P < 0'05
'Shoot and root weights of chickpea, lupins and peas are means of 5 plants from each replicate pot, while other treatments show means fram 10 plants in each pot.
M. M. Dewan and K. Sivasithamparam
159
Fig. 3. Roots of wheat with (A) and without (B) colorization by the sterile red fungus, 3 wk after planting.
(A)
RESULTS
Soil moisture and temperature The SRF protected wheat and rye-grass from infection by the take-all fungus at both levels of soil water potential (- 0'0015 and - 0'001 MPa) and temperature (15 and 20°) (Fig. 1 A, B). In Ggt-alone treatments, the percentage of dead plants of wheat and rye-grass was greater at - 0'0015 MPa than at - 0'001 MPa. The isolate of Ggt was more pathogenic on wheat than on rye-grass. The SRF promoted growth of wheat and rye-grass in the SRF alone and SRF + Ggt treatments at - 0'0015 and - 0'001 MPa and at 15 and 20°, but promotion over controls was greatest at - 0'001 MPa and 15° for wheat. and at - 0'001 MPa and 20° for rye-grass. The reductions of shoot and root weights of wheat and ryegrass caused by the take-all fungus were most severe at - 0'0015 MPa and 20° (Table 1). Under all conditions, the roots of wheat and rye-grass were extensively rotted in Ggt-alone treatments, but the greatest damage on wheat and rye-grass occurred at - 0'0015 MPa and 20° (Fig. 2). The SRF caused no damage to the roots of wheat or rye-grass in SRF-alone treatment. while some symptoms of take-all disease was evident on the roots of wheat in SRF + Ggt treatment at - 0'0015 MPa and 15 or 20°. This effect. however, was not reflected in the shoot and root weights.
(B)
extent of colonization. The recovery of the SRF was more frequent from the roots of wheat. rye-grass, oats, barley and great brome than peas, lupins, medic, subterranean clover and chick pea (Fig. 4).
Fig. 4. Percentage of root pieces of barley (B), great brome (G.B.), chickpea (C), subterranean dover (S.c.), lupins (L). medic (M), oats (0), peas (P), rape (R), rye-grass (R.G.) and wheat (W) yielding sterile red fungus (SRF) after being planted in soil infested with SRF for 4 wk. Bar shows L.S.v.. P < 0'05.
Host range The SRF increased the shoot and root fresh weights of barley, great brome, chick pea, lupins, medic, oats, peas, rape, ryegrass, subterranean clover and wheat (Table 2). Although the roots of all these plants were found to be infected and covered by the SRF (Fig. 3), some differences were evident in the
B G.B. C S.c. L
MOP
R R.G. W
Effect of a sterile fungus on rotation crops and take-all Growth promotion by the SRF on these hosts was very pronounced three weeks after planting.
160 Glenn for advice on water relations. One of us (M. M. D.) was supported by a generous grant from the Ministry of Higher Education, Government of Iraq.
DISCUSSION The SRF appeared to be active at both levels of soil moisture and temperature. These were chosen to match those that prevail in the Western Australian grain belt at the beginning of the cropping season (May/June). As these soil conditions are equally suitable for the activity of the SRF as they are for the take-all fungus (Sivasithamparam & Parker, 1981), the SRF should compete effectively with the take-all fungus in and around the wheat roots in the field if all other conditions are favourable. In several aspects the suitability of SRF as a biocontrol agent resembles that of Laetisaria arvahs Burdsall, which also was originally isolated as a sterile fungus (Burdsall et al., 1980). Hoch & Abawi (1979) found that L. arvahs was active over the range of temperatures and moistures that favour the high incidence of. and damage caused by, Pythium disease. They found that L. arvahs was non-pathegenic to a range of crop plants commonly grown in rotation with beet and that it was also easy to produce large amounts of inoculum for use against plant pathogens. Another attractive feature about the SRF is that in addition to its ability to produce antibiotics (Dewan & Sivasithamparam, 1989), it colonizes the root cortex rapidly (Dewan & Sivasithamparam, unpub!.), unlike Trichoderma spp. which appear to preferentially colonize soil and commonly inhabit soils having high moisture content (Baker & Cook, 1974). This study also showed that the roots of graminaceous plants were covered more rapidly and extensively by the mycelia of the SRF than those of other crops. Although the SRF appears to show preference for the roots of certain plants it was non-pathogenic to all those tested, indicating that if used as an inoculant of wheat it is unlikely to cause damage to any of the crops which are grown in rotation with wheat in Western Australia. We wish to thank Mr A. Ali, Mr T. Armitage, Mr H. Saoub, Mr M. Munasley for their valuable assistance and Mrs O. (Received for publication 17 May 1988)
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DEWAN, M. M. & SIVASITHAMPARAM, K. (1989). Behaviour of a plant growth promoting sterile fungus on agar and roots of ryegrass and wheat. Mycological Research 93, 161-166. HALL, G. (1987). SEM studies of sterile fungi on roots of sterile wheat seedlings. Transactions of the British Mycological Society 88, 549-553.
HOCH, H. C. & ABAWI, G. S. (1979). Biological control of Pythium root rot of table beets with Corticium sp. Phytopathology 69, 417-419.
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WAlD, j. S. (1974). The decomposition of roots. In The Biology of Plant Litter Decomposition 1 (ed. C. H. Dickinson & G. j. F. Pugh), pp. 175-210. London: Academic Press.