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Growth and infectivity of Gaeumannomyces graminis var. tritici in soil
Soil Bid.
Biochem. Vol. 20, No. 4, pp. 515-576,
1988
0038-0717/88
Printed in Great Britain. All rights reserved
$3.00 + 0.00
Copyright 0 1988Pergamon Press plc
SHORT COMMUNICATION GROWTH
AND INFECTIVITY OF GAEUMANNOMYCES VAR. TRITICI IN SOIL
GRAMINIS
0. F. GLENN and C. A. PARKER Soil Science and Plant Nutrition Group, School of Agriculture, The University of Western Australia, Nedlands, Western Australia 6009 (Accepted 25 November 1987)
The rapid spread of the take-all disease into soils farmed to wheat has been described by Winter (1939) and Gerlagh (1968). The mechanisms postulated have been growth along wheat roots in the rows (White, 1942) and aerial dispersal of ascospores (Gerlagh, 1968). The ability of the take-all fungus to grow in soil up to 4cm from infected straw pieces at low temperatures and with ample soil water was described by Grose et al. (1984) whose results also indicated suppression of growth of Gueumannomyces gruminis var. Wici (Ggt) by soil organisms at higher temperatures. This method involved growth of the fungus on a membrane between two layers of soil. This technique is open to the criticism that the fungus would use the membrane surface as an aid to lateral growth but would not otherwise be able to grow through soil. The common perception of Ggt is that of a near obligate pathogen with low competitive saprophytic ability (Garrett, 1956). In a review of this area Shipton ( 1981) concluded that “mycelium of Ggt has an unmistakable, though limited, capacity for saprophytic growth through soil”. We have found that the hyphae of Ggt can grow a considerable distance through soil and are capable of infecting wheat roots with which they come into contact.
Experiments established that wheat roots failed to penetrate a triple-layered stainless steel wire mesh cylinder during the growing period. These cylinders were composed of two layers of 99.1 pm hole size mesh and one of 602 pm for rigidity (Boral-melwire). Cylinders of 6 or 9 cm dia were placed upright on the floor of 3 kg pots (Fig. IA) which were tilled with 2.5 kg of a 1: 1 mixture of yellow sand and Gabalong soil (Sivasithamparam ef al., 1979). The soil was maintained at 55% saturated water holding capacity. Two groups of three wheat seedlings were planted outside each cylinder diametrically opposite each other. Sterile straw pieces were infested with Ggt by placing them around a colony of Ggt growing on 0.04% malt extract broth agar containing 133 pg streptomycin ml-‘. The fungus was allowed 4 weeks at 17°C to colonize the 7 mm straw pieces. Ggt-infested straw pieces were buried 2 cm deep inside the cylinders so that there were different distances between the inoculum and the seedlings (Fig. 1B). The pots were stood in a root-cooling tank of water which kept the soil temperature between 12.5 and 20°C at 2 cm; and between 10.5 and 12.5”C at IOcm. Plants were harvested after 5 and 8 weeks. Their roots were scored for disease according to the location and severity of the lesion on a scale from
A. Layout within Treatment
stelnlesssteel,biple layer
soil lavaI
mash cylkidar
wheat seedlings
Ggt-infested wheat straw f2cm beneath surface1
2.5kg soil mixture -
3kg o&tic pot
B. Positioning of Straw Pieces
TFtEATMENT 1
TFtEATMENT 2 Fig. 1 575
TREATMENT 3
TREATMENT 4
Short communications
576
Table I. Take-all root lesion rating scheme Lesion rating 0 OS
I .o 2.0 2.5 3.0 4.0 5.0
Description No sign of infection Dark flecks on roots Stele discoloured in a few fine lateral roots Many fine lateral roots infected Some stelar discoloration in seminal roots One seminal root completely blocked Two seminal roots blocked close to the crown Four or more seminal roots blocked close to the crown
Table 2. Severity of infection of Ggt on wheat roots grown in Gabalong soil-river sand mixture Distance between seed and inoculum (cm)
Range of root lesion rating (54 plants) after 5 weeks
I
4.0-5.0 ND I .&5.0 ND 0.0 ND ND ND
2 3 4 5 6 7 8
Mean
Range of root lesmn rating (2-8 plants) after 8 weeks
Mean
4.83 ND 3.33 ND 0.00 ND ND ND
4.5-5.0 I .&5.0 o&4.0 0.0-I .o 0.0-I .o O&3.0 0.0 0.0
4.8 I 3.81 2.58 0.5 0.2 0.67 0.00 0.00
ND = not determined.
0 to 5 devised by P. Cotterill (personal communication; Table 1). In this experiment hyphae grew up to 6 cm through soil and infected wheat roots (Table 2). The frequency and severity of infection was less the further the fungus had to travel. These data support the observations of Wildermuth et al. (1984) using a different technique, that the rate of growth of Ggt in soil can be of the order of 0.4-0.6mm day-‘. Our data show that, under the soil conditions used, the fungus can grow through soil, retaining sufficient inoculum potential to form lesions on wheat roots 60 mm from the original inoculum. It would seem likely that saprophytic growth could play an important part in the spread of disease through a crop. Acknowledgement-We thank the Rural Credits Development Fund of the Reserve Bank of Australia whose financial support permitted the completion of this investigation.
REFERENCES Garrett S. D. (1956) Biology of Roof-infecting Fungi. Cambridge University Press, Camb. Gerlagh M. (1968) Introduction of Ophiobolus graminis into
new polders and its decline. Communication No. 241, Laboratory of Phytopathology, Agricultural University, Wageningen. Grose M. J., Parker C. A. and Sivasithamparam K. (1984) Growth of Gaeumannomyces gruminis var. rritici in soil: effects of temperature and water potential. Soil Biology & Biochemistry 16, 211-216. Shipton P. J. (1981) Saprophytic survival. In Biology and Control of Take-all (M. J. C. Asher and P. J. Shipton, Eds), pp. 295-316. Academic Press, London. Sivasithamparan K., Parker C. A. and Edwards C. S. (1979) Rhizosphere microorganisms of seminal and nodal roots of wheat grown in pots. Soil Biology & Biochemistry 11, 155-160.
White N. H. (1942) The genetics of Ophiobolus gramini3 Sacc. 1. Heritable variations for culture colour and patho. genicity. Journal of the Councilfor Scienrific and Industria. Research (Ausfralia) 15, 118-124. Wildermuth G. B.. Warcup J. H. and Rovira A. D. (1984 Growth of Gaeumannomyces graminis var. tririci in soil ir the presence and absence of wheat roots. Transaclions o_ the British Mycological Society 82, 435-441.
Winter A. G. (1939) Der Einfluss det physikalischel Bodenstruktur auf den lnfektionsverlauf bei der Ophio bolose des Weizens. Zierschrift fuer Pfianzenkrankheiten Ppanzen Pathologic. Pfanzen &hut-_ 39, 5 13-5 19.
Biochem. Vol. 20, No. 4, pp. 515-576,
1988
0038-0717/88
Printed in Great Britain. All rights reserved
$3.00 + 0.00
Copyright 0 1988Pergamon Press plc
SHORT COMMUNICATION GROWTH
AND INFECTIVITY OF GAEUMANNOMYCES VAR. TRITICI IN SOIL
GRAMINIS
0. F. GLENN and C. A. PARKER Soil Science and Plant Nutrition Group, School of Agriculture, The University of Western Australia, Nedlands, Western Australia 6009 (Accepted 25 November 1987)
The rapid spread of the take-all disease into soils farmed to wheat has been described by Winter (1939) and Gerlagh (1968). The mechanisms postulated have been growth along wheat roots in the rows (White, 1942) and aerial dispersal of ascospores (Gerlagh, 1968). The ability of the take-all fungus to grow in soil up to 4cm from infected straw pieces at low temperatures and with ample soil water was described by Grose et al. (1984) whose results also indicated suppression of growth of Gueumannomyces gruminis var. Wici (Ggt) by soil organisms at higher temperatures. This method involved growth of the fungus on a membrane between two layers of soil. This technique is open to the criticism that the fungus would use the membrane surface as an aid to lateral growth but would not otherwise be able to grow through soil. The common perception of Ggt is that of a near obligate pathogen with low competitive saprophytic ability (Garrett, 1956). In a review of this area Shipton ( 1981) concluded that “mycelium of Ggt has an unmistakable, though limited, capacity for saprophytic growth through soil”. We have found that the hyphae of Ggt can grow a considerable distance through soil and are capable of infecting wheat roots with which they come into contact.
Experiments established that wheat roots failed to penetrate a triple-layered stainless steel wire mesh cylinder during the growing period. These cylinders were composed of two layers of 99.1 pm hole size mesh and one of 602 pm for rigidity (Boral-melwire). Cylinders of 6 or 9 cm dia were placed upright on the floor of 3 kg pots (Fig. IA) which were tilled with 2.5 kg of a 1: 1 mixture of yellow sand and Gabalong soil (Sivasithamparam ef al., 1979). The soil was maintained at 55% saturated water holding capacity. Two groups of three wheat seedlings were planted outside each cylinder diametrically opposite each other. Sterile straw pieces were infested with Ggt by placing them around a colony of Ggt growing on 0.04% malt extract broth agar containing 133 pg streptomycin ml-‘. The fungus was allowed 4 weeks at 17°C to colonize the 7 mm straw pieces. Ggt-infested straw pieces were buried 2 cm deep inside the cylinders so that there were different distances between the inoculum and the seedlings (Fig. 1B). The pots were stood in a root-cooling tank of water which kept the soil temperature between 12.5 and 20°C at 2 cm; and between 10.5 and 12.5”C at IOcm. Plants were harvested after 5 and 8 weeks. Their roots were scored for disease according to the location and severity of the lesion on a scale from
A. Layout within Treatment
stelnlesssteel,biple layer
soil lavaI
mash cylkidar
wheat seedlings
Ggt-infested wheat straw f2cm beneath surface1
2.5kg soil mixture -
3kg o&tic pot
B. Positioning of Straw Pieces
TFtEATMENT 1
TFtEATMENT 2 Fig. 1 575
TREATMENT 3
TREATMENT 4
Short communications
576
Table I. Take-all root lesion rating scheme Lesion rating 0 OS
I .o 2.0 2.5 3.0 4.0 5.0
Description No sign of infection Dark flecks on roots Stele discoloured in a few fine lateral roots Many fine lateral roots infected Some stelar discoloration in seminal roots One seminal root completely blocked Two seminal roots blocked close to the crown Four or more seminal roots blocked close to the crown
Table 2. Severity of infection of Ggt on wheat roots grown in Gabalong soil-river sand mixture Distance between seed and inoculum (cm)
Range of root lesion rating (54 plants) after 5 weeks
I
4.0-5.0 ND I .&5.0 ND 0.0 ND ND ND
2 3 4 5 6 7 8
Mean
Range of root lesmn rating (2-8 plants) after 8 weeks
Mean
4.83 ND 3.33 ND 0.00 ND ND ND
4.5-5.0 I .&5.0 o&4.0 0.0-I .o 0.0-I .o O&3.0 0.0 0.0
4.8 I 3.81 2.58 0.5 0.2 0.67 0.00 0.00
ND = not determined.
0 to 5 devised by P. Cotterill (personal communication; Table 1). In this experiment hyphae grew up to 6 cm through soil and infected wheat roots (Table 2). The frequency and severity of infection was less the further the fungus had to travel. These data support the observations of Wildermuth et al. (1984) using a different technique, that the rate of growth of Ggt in soil can be of the order of 0.4-0.6mm day-‘. Our data show that, under the soil conditions used, the fungus can grow through soil, retaining sufficient inoculum potential to form lesions on wheat roots 60 mm from the original inoculum. It would seem likely that saprophytic growth could play an important part in the spread of disease through a crop. Acknowledgement-We thank the Rural Credits Development Fund of the Reserve Bank of Australia whose financial support permitted the completion of this investigation.
REFERENCES Garrett S. D. (1956) Biology of Roof-infecting Fungi. Cambridge University Press, Camb. Gerlagh M. (1968) Introduction of Ophiobolus graminis into
new polders and its decline. Communication No. 241, Laboratory of Phytopathology, Agricultural University, Wageningen. Grose M. J., Parker C. A. and Sivasithamparam K. (1984) Growth of Gaeumannomyces gruminis var. rritici in soil: effects of temperature and water potential. Soil Biology & Biochemistry 16, 211-216. Shipton P. J. (1981) Saprophytic survival. In Biology and Control of Take-all (M. J. C. Asher and P. J. Shipton, Eds), pp. 295-316. Academic Press, London. Sivasithamparan K., Parker C. A. and Edwards C. S. (1979) Rhizosphere microorganisms of seminal and nodal roots of wheat grown in pots. Soil Biology & Biochemistry 11, 155-160.
White N. H. (1942) The genetics of Ophiobolus gramini3 Sacc. 1. Heritable variations for culture colour and patho. genicity. Journal of the Councilfor Scienrific and Industria. Research (Ausfralia) 15, 118-124. Wildermuth G. B.. Warcup J. H. and Rovira A. D. (1984 Growth of Gaeumannomyces graminis var. tririci in soil ir the presence and absence of wheat roots. Transaclions o_ the British Mycological Society 82, 435-441.
Winter A. G. (1939) Der Einfluss det physikalischel Bodenstruktur auf den lnfektionsverlauf bei der Ophio bolose des Weizens. Zierschrift fuer Pfianzenkrankheiten Ppanzen Pathologic. Pfanzen &hut-_ 39, 5 13-5 19.