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Interactions between mycophagous nematodes, mycorrhizal and other soil fungi
163
Agriculture, Ecosystems and Environment, 29 (1989) Elsevier Science Publishers B.V., Amsterdam Printed in Czechoslovakia
163-167
INTERACTIONS BETWEEN MYCOPHAGOUS NEMATODES, MYCORRHIZAL AND OTHER SOIL FUNGI NIKOS GIANNAKIS, FRANCIS E. SANDERS
Department of Pure and AppliedBiology, The University,Leeds !.32 9JT, England ABSTRACT Three species of mycophagous nematodes were able to feed and multiply, and in the process damage the mycelium of a range of fungi in pure culture. The fungi preferred by the nematodes included some ectomycorrhizal species. When mycorrhizal plants were grown in soil where nematode numbers were high due to the presence in the soil of actively growing mycelium of Agaricus bisporus, some effect of the nematodes could occasionally be detected, in particular reduction of phosphorus uptake and yield of the host plant. There was no significant effect on.levels of mycorrhizal infection. INTRODUCTION The beneficial effects of VAM fungi on the yield of crops have been extensively documented (Ha~ley and Smith 1983). However, in field experiments responses of plants to mycorrhizal infection are not always significant (Ross and Harper 1970). This may be due in part to damage to external mycelium by mycophagous soil fauna if:inlay 1985). In one of the few papers dealing with effects of mycophagous nematodes on mycorrhizaJ systems, Hussey and Roncadori (1981) found that the yield of mycorrhizal cott.on was occa:;ionally reduced by nematodes applied in high numbers but mycorrhizaJ infection was unaffected. In our own experiments, when nematodes were aoded to soil containing mycelium of Glomus clarum in association with mycorrhizal clover roots, numbers of nematodes declined and them were no adverse effects on the host. Soil fungi other than VAM (including ectomycorrhizal species) can sustain large populations of mycophagous nematodes (Ingham et al. 1985, Riffle 1971) which may influence the development of the VAM symbiosis in agricultural soils Wheresapmtrophic fungi are often abundant. The ainl of the work reported here was to study quantitatively the following: 1. 'The food preferences of three selected species of nematodes growing on pure cultures of various saprotrophic and ectomycorrhizal fungi. 2. The intera(.tiQns in soil between ~d clover O'rifoliumpratense), Glomus clarum (Gc), and mycophagous nematodes whose populations can be maintained at high levels if saprotrophic fungi are also present.
164
MATERIAL AND METHODS Ex~rlment l Peui dishes containing equal amounts of potato dextrose agar were inoculated with ~ne of the. following species of fungi: Agaricus bisporus (Ab), Rhizoctonia $olani (Rs), Laccaria laccata (LI)o~
Hebeloma crl~tuliniforme (He), Rhizopogon roseolus (Rr), PaxUlus involutus (Pi), Cenococcum graniforme (Cg) and an unidentified saprotrophic species (D). Once growth of~he fungi had started, some plates were inoculated in triplicate with approximately 700 Aphelenchoidescomposticola(Ac), Aphelenchus avenae (An) or Diryl'enchus myceliophagus (Din). Control plates did not receive nematodes. The dishes were incubated at 20 °C. 50 days Lfter the inoculation with fungi, mycelia and nematodes were exlxacted by melting the agar in water at 100 °C and passing it through a 2:~0 pm sieve to separate fungal mycelium from nematodes. The mycelium was dried at 95 °C a,~d weighed and the nematodes were counted by sampling the sieved suspension, Experiment 2 Clover plants were grown in amended soil (200 g of a mixture of calcareous sandy loam with coarse sand at a 1:1 ratio, low in available phosphorus and partially sterilised by heat). In addition, each pot received a layer of 2 g of sterile bran (bran Ireatmen0 or bran colonised by mycelium of Ab (Ab Ireatmen0 or no bran at all (control) plus a layer of live mycorrhizal inoculum (Gc treatments) or sterile inoculum and leachings of live inoculum (-Uc treatments). Nematode treatments received Ac at a rate of 5/g soil. All treatments had 15 replicates. Pots were placed randomly in a growth room set at 16 h light (photon flux density = 310 ~mol m'2s "1, 25 °C) and 8 h dark (20 °C) with relative humidity of 70 %. $ pots of each treatment were harvested on three occasions. Dry weights of shoots ~ d roots were recorded and nematodes were recovered (modified Baermann funnel) and counted. The efficiency of the r e ~ v v ~ procedure was 83 % (coefficient of variation 4 %). Mycorrhizal infection was estimated using the gridline intersect method after staining roots with trypan blue-lactophenol. The phosphorus content of shoots .was measured (vanado-molybdate method following dry combustion). RESULTS AND DISCUSSION The effect.~of nematodes on the growth of fungal mycelia are illustrated in figure I. Dm multiplied to the least extent and had the smallest effect on the mycelial weight. Ac reduced mycelial weights to the greatest extent and multiplied much better than Aa or Dm (figure I and plate I). In contrast to Dm orAc, Aa did not feed or reproduce on Rr and Dm did not feed on severa~ of the /regal species tested. The greatest reductions in weights of mycelium were not always correlated with numbers of nematodes which indicated that some fungi were more easily damaged than others.
Ac had the widest range of fungal hosts and was therefore chosen as the most appropriate species to employ in our study of the effect of mycophagy on the VAM fungus Gc, whose suitability as a nematode host could not be assessed in pure culture.
t65
PLATE 1. An example of the effect of mycophagousnematodeson the •myceliumof the ectomycorghizalfungusPaxillus involutus (Pi). Ac =Aphelenchoide$ compo$1icola.Aa= Apheleachus avenae and Dm= Dirylenchusmyceliopha&us.
Ex~fiment 2 Ingham et al. (,~85) found that mycophagous nemat~les did not affect the yield of plants growing in soils with saprotrophic fungi which agrees with o ~ results where Ac did not influence the growth of non-mycorrhizal plants treated with Ab. Mycorrhizal plants in the second and third harvest were nearly 90 % heavier than controls. All pots containing Ab had significantly higher nematode numbers, associated with a reduction in the yield of mycorrhizal plants at harvest 2. P
166
all p~atesreceived 700 nem-'qode~ 10" xlO s 8"
i
|
2-
I=
80 60 'R
.I
2o o
[]
.20
ab
cg
d
hc !1 pi species of fungus
rr
rs
FiGUI~ 1. Experimen~1: the reproductionofthe nematodeson differentspecies of fungiand damage to (he fungal myceU~.
. content in the shoots of mycorrhizal plants was also reduced at harvest 2, but there was no significant effect on ~ mycorrhizal infection. We conclude that nematodes may have reduced the growth of mycorrhizal plai~s by repx~xlucing on Ab and then attacking the external mycelium of the VAM fungus, thus hindering the uptake of phosphate by the mycon'hizal plants. There is a clear negative effect of mycophagous nematodes on the growth of saprotrophic fungi and nematodes are able to reproduce profusely. Damage to ectomycorrhizal mycelia may be of major significance For the establishment of ectomycorrhizas, Nematodes showed marked food preferences. In soil treated with Gc alone, Ac reproducc.d only slightly compared to the case where Ab was prcsenL Only after reaching unu~ually high numbers in the presence of Ab could 4c have a negative effect on mycorrhizal red clover. This effect was significant only at a certain stage of plant growth and
167
was of minor importance compared to the consistent growth stimulation by Gc. There is therefore some evidence that saprotrophic fungi which can serve as hosts for mycophagous nematodes may indirectly influence the development of VA mycorrhizas in the field, but such effects are likely to be small. REFERENCES FINLAY, R.D.: Interactions between soil micro-arthropods and endomycorrhizal associations of higher plants. In: FITTER, A.H./ed./: Ecological interactions in soil. Pp. 319-331. Brit. Ecol. Soc., London 1985. HARLEY, J.L., SMITH, S.E.: Mycorrhizal Symbiosis. Academic Press, London 1983. HUSSEY, R.S., RONCADORI, R.W.: Influence of Aphelenchus avenae on vesicular-arbuscular endomycorrhizal growth response in cotton. Journal of Nematology 13: 48-52, 1981. INGHAM, R.E., TROFYMOW, J.A., INGHAM, E.R., COLEMAN, D.C.: Interactions of bacteria, fungi, and their nematode grazers: Effects on nutrient cycling and plant growth. Ecological Monographs 55:119-140, 1985. RIFFLE, J.W.: Effect of nematodes on root-inhabiting fungi. In: HACSKAYLO E. /ed./: Proceedings of the I st North American Conference on Mycorrhizae. Pp. 97-113. U.S. Dept. of Agriculture. ROSS, J.P., HARPER, J.A.: Effect of Endosone mycorrhiza on soybean yield. Phytopathology 60: 1552-1556, 1970.
Giannakis, N. and s a n d e r s e F . E . , 1989: I n t e r a c t i o n s between mycophagous nematodes, mycorrhizal and o t h e r eoXl f u n g i . & g r i t . E c o s y s t e m s E n v i r o n . e 29: 1 6 3 - 1 6 7 .
Agriculture, Ecosystems and Environment, 29 (1989) Elsevier Science Publishers B.V., Amsterdam Printed in Czechoslovakia
163-167
INTERACTIONS BETWEEN MYCOPHAGOUS NEMATODES, MYCORRHIZAL AND OTHER SOIL FUNGI NIKOS GIANNAKIS, FRANCIS E. SANDERS
Department of Pure and AppliedBiology, The University,Leeds !.32 9JT, England ABSTRACT Three species of mycophagous nematodes were able to feed and multiply, and in the process damage the mycelium of a range of fungi in pure culture. The fungi preferred by the nematodes included some ectomycorrhizal species. When mycorrhizal plants were grown in soil where nematode numbers were high due to the presence in the soil of actively growing mycelium of Agaricus bisporus, some effect of the nematodes could occasionally be detected, in particular reduction of phosphorus uptake and yield of the host plant. There was no significant effect on.levels of mycorrhizal infection. INTRODUCTION The beneficial effects of VAM fungi on the yield of crops have been extensively documented (Ha~ley and Smith 1983). However, in field experiments responses of plants to mycorrhizal infection are not always significant (Ross and Harper 1970). This may be due in part to damage to external mycelium by mycophagous soil fauna if:inlay 1985). In one of the few papers dealing with effects of mycophagous nematodes on mycorrhizaJ systems, Hussey and Roncadori (1981) found that the yield of mycorrhizal cott.on was occa:;ionally reduced by nematodes applied in high numbers but mycorrhizaJ infection was unaffected. In our own experiments, when nematodes were aoded to soil containing mycelium of Glomus clarum in association with mycorrhizal clover roots, numbers of nematodes declined and them were no adverse effects on the host. Soil fungi other than VAM (including ectomycorrhizal species) can sustain large populations of mycophagous nematodes (Ingham et al. 1985, Riffle 1971) which may influence the development of the VAM symbiosis in agricultural soils Wheresapmtrophic fungi are often abundant. The ainl of the work reported here was to study quantitatively the following: 1. 'The food preferences of three selected species of nematodes growing on pure cultures of various saprotrophic and ectomycorrhizal fungi. 2. The intera(.tiQns in soil between ~d clover O'rifoliumpratense), Glomus clarum (Gc), and mycophagous nematodes whose populations can be maintained at high levels if saprotrophic fungi are also present.
164
MATERIAL AND METHODS Ex~rlment l Peui dishes containing equal amounts of potato dextrose agar were inoculated with ~ne of the. following species of fungi: Agaricus bisporus (Ab), Rhizoctonia $olani (Rs), Laccaria laccata (LI)o~
Hebeloma crl~tuliniforme (He), Rhizopogon roseolus (Rr), PaxUlus involutus (Pi), Cenococcum graniforme (Cg) and an unidentified saprotrophic species (D). Once growth of~he fungi had started, some plates were inoculated in triplicate with approximately 700 Aphelenchoidescomposticola(Ac), Aphelenchus avenae (An) or Diryl'enchus myceliophagus (Din). Control plates did not receive nematodes. The dishes were incubated at 20 °C. 50 days Lfter the inoculation with fungi, mycelia and nematodes were exlxacted by melting the agar in water at 100 °C and passing it through a 2:~0 pm sieve to separate fungal mycelium from nematodes. The mycelium was dried at 95 °C a,~d weighed and the nematodes were counted by sampling the sieved suspension, Experiment 2 Clover plants were grown in amended soil (200 g of a mixture of calcareous sandy loam with coarse sand at a 1:1 ratio, low in available phosphorus and partially sterilised by heat). In addition, each pot received a layer of 2 g of sterile bran (bran Ireatmen0 or bran colonised by mycelium of Ab (Ab Ireatmen0 or no bran at all (control) plus a layer of live mycorrhizal inoculum (Gc treatments) or sterile inoculum and leachings of live inoculum (-Uc treatments). Nematode treatments received Ac at a rate of 5/g soil. All treatments had 15 replicates. Pots were placed randomly in a growth room set at 16 h light (photon flux density = 310 ~mol m'2s "1, 25 °C) and 8 h dark (20 °C) with relative humidity of 70 %. $ pots of each treatment were harvested on three occasions. Dry weights of shoots ~ d roots were recorded and nematodes were recovered (modified Baermann funnel) and counted. The efficiency of the r e ~ v v ~ procedure was 83 % (coefficient of variation 4 %). Mycorrhizal infection was estimated using the gridline intersect method after staining roots with trypan blue-lactophenol. The phosphorus content of shoots .was measured (vanado-molybdate method following dry combustion). RESULTS AND DISCUSSION The effect.~of nematodes on the growth of fungal mycelia are illustrated in figure I. Dm multiplied to the least extent and had the smallest effect on the mycelial weight. Ac reduced mycelial weights to the greatest extent and multiplied much better than Aa or Dm (figure I and plate I). In contrast to Dm orAc, Aa did not feed or reproduce on Rr and Dm did not feed on severa~ of the /regal species tested. The greatest reductions in weights of mycelium were not always correlated with numbers of nematodes which indicated that some fungi were more easily damaged than others.
Ac had the widest range of fungal hosts and was therefore chosen as the most appropriate species to employ in our study of the effect of mycophagy on the VAM fungus Gc, whose suitability as a nematode host could not be assessed in pure culture.
t65
PLATE 1. An example of the effect of mycophagousnematodeson the •myceliumof the ectomycorghizalfungusPaxillus involutus (Pi). Ac =Aphelenchoide$ compo$1icola.Aa= Apheleachus avenae and Dm= Dirylenchusmyceliopha&us.
Ex~fiment 2 Ingham et al. (,~85) found that mycophagous nemat~les did not affect the yield of plants growing in soils with saprotrophic fungi which agrees with o ~ results where Ac did not influence the growth of non-mycorrhizal plants treated with Ab. Mycorrhizal plants in the second and third harvest were nearly 90 % heavier than controls. All pots containing Ab had significantly higher nematode numbers, associated with a reduction in the yield of mycorrhizal plants at harvest 2. P
166
all p~atesreceived 700 nem-'qode~ 10" xlO s 8"
i
|
2-
I=
80 60 'R
.I
2o o
[]
.20
ab
cg
d
hc !1 pi species of fungus
rr
rs
FiGUI~ 1. Experimen~1: the reproductionofthe nematodeson differentspecies of fungiand damage to (he fungal myceU~.
. content in the shoots of mycorrhizal plants was also reduced at harvest 2, but there was no significant effect on ~ mycorrhizal infection. We conclude that nematodes may have reduced the growth of mycorrhizal plai~s by repx~xlucing on Ab and then attacking the external mycelium of the VAM fungus, thus hindering the uptake of phosphate by the mycon'hizal plants. There is a clear negative effect of mycophagous nematodes on the growth of saprotrophic fungi and nematodes are able to reproduce profusely. Damage to ectomycorrhizal mycelia may be of major significance For the establishment of ectomycorrhizas, Nematodes showed marked food preferences. In soil treated with Gc alone, Ac reproducc.d only slightly compared to the case where Ab was prcsenL Only after reaching unu~ually high numbers in the presence of Ab could 4c have a negative effect on mycorrhizal red clover. This effect was significant only at a certain stage of plant growth and
167
was of minor importance compared to the consistent growth stimulation by Gc. There is therefore some evidence that saprotrophic fungi which can serve as hosts for mycophagous nematodes may indirectly influence the development of VA mycorrhizas in the field, but such effects are likely to be small. REFERENCES FINLAY, R.D.: Interactions between soil micro-arthropods and endomycorrhizal associations of higher plants. In: FITTER, A.H./ed./: Ecological interactions in soil. Pp. 319-331. Brit. Ecol. Soc., London 1985. HARLEY, J.L., SMITH, S.E.: Mycorrhizal Symbiosis. Academic Press, London 1983. HUSSEY, R.S., RONCADORI, R.W.: Influence of Aphelenchus avenae on vesicular-arbuscular endomycorrhizal growth response in cotton. Journal of Nematology 13: 48-52, 1981. INGHAM, R.E., TROFYMOW, J.A., INGHAM, E.R., COLEMAN, D.C.: Interactions of bacteria, fungi, and their nematode grazers: Effects on nutrient cycling and plant growth. Ecological Monographs 55:119-140, 1985. RIFFLE, J.W.: Effect of nematodes on root-inhabiting fungi. In: HACSKAYLO E. /ed./: Proceedings of the I st North American Conference on Mycorrhizae. Pp. 97-113. U.S. Dept. of Agriculture. ROSS, J.P., HARPER, J.A.: Effect of Endosone mycorrhiza on soybean yield. Phytopathology 60: 1552-1556, 1970.
Giannakis, N. and s a n d e r s e F . E . , 1989: I n t e r a c t i o n s between mycophagous nematodes, mycorrhizal and o t h e r eoXl f u n g i . & g r i t . E c o s y s t e m s E n v i r o n . e 29: 1 6 3 - 1 6 7 .