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Ecology of nematophagous fungi in agricultural soils

Persmark, Lotta LU (1997)
Abstract (Swedish)
Popular Abstract in Swedish

Nematofaga svampar förekommer inom många grupper i svampriket och har den gemensamma förmågan att döda nematoder (millimeterstora rundmaskar) och använda dem som näring. Vissa arter är obligata parasiter, medan andra är fakultativa saprofyter, vilket innebär att de förutom att parasitera nematoder lever av dött organiskt material. Dessa svampar har, sedan de upptäcktes för ca 100 hundra år sen, fascinerat biologer p.g.a. sina intrikata metoder att fånga nematoder. Dessutom har de nematofaga svamparna en potential för biologisk kontroll av både växt- och djurparasitära nematoder, vilket har föranlett forskning inom detta område. Hittills finns det dock inga exempel på tillämpningar av de... (More)
Popular Abstract in Swedish

Nematofaga svampar förekommer inom många grupper i svampriket och har den gemensamma förmågan att döda nematoder (millimeterstora rundmaskar) och använda dem som näring. Vissa arter är obligata parasiter, medan andra är fakultativa saprofyter, vilket innebär att de förutom att parasitera nematoder lever av dött organiskt material. Dessa svampar har, sedan de upptäcktes för ca 100 hundra år sen, fascinerat biologer p.g.a. sina intrikata metoder att fånga nematoder. Dessutom har de nematofaga svamparna en potential för biologisk kontroll av både växt- och djurparasitära nematoder, vilket har föranlett forskning inom detta område. Hittills finns det dock inga exempel på tillämpningar av de nematofaga svamparna för biologisk kontroll i stor skala. Detta kan, till stor del, bero på att vi har dåliga kunskaper om deras biologi i sin naturliga miljö. Målet med arbetet i denna avhandling var att öka kunskapen om de nematofaga svamparnas ekologi i jordbruks mark. Under en treårs fältstudie undersöktes mängden och artsammansättningen av nematod-fångande svampar och sammanlagt hittades 13 arter. Mellan 10 och 1000 propaguler (sporer och hyffragment) nematod-fångande svampar g-1 jord uppmättes och den vanligast förekommande arten var Arthrobotrys oligospora. De största svampmängderna fanns i de översta 10 centimeters jordlagret. Mängden nematodfångande svamp varierade över säsongen och de största mängderna uppmättes på sensommaren och hösten. I rotzonen hos ärt var mängden svamp ca 5-20 gånger större än i den rotfria jorden. Upp till 0,3% av nematoderna var infekterade med endoparasitära nematofaga svampar, och den vanligast förekommande arten var Catenaria anguillulae. Relationen mellan naturligt förekommande nematofaga svampar och nematoder undersöktes genom populationsstudier i jordbruksmark. Förekomsten av de mer parasitära nematodfångande svamparna samt de endoparasitära svamparna minskade drastiskt under en treårs period samtidigt som antalet nematoder minskade med hälften. Detta tyder på att de mer parasitära svamparna för att tillväxa kräver en mängd nematoder över en viss tröskelnivå. Å andra sidan påverkades inte mängden saprofytiska nematodfångande svampar när antalet nematoder minskade, vilket tyder på att dessa inte är beroende av nematoder i marken. Bevis för att de nematofaga svamparna reglerar antalet nematoder i marken erhölls inte i arbetet med denna avhandling. T ex hade mängden nematodfångande svampar och mängden nematoder en liknande säsongsvariation, men de var inte korrelerade till varandra. Vidare var mängden nematodfångande svampar inte relaterad till mängden nematoder. Övergången mellan den saprofytiska och den parasitära fasen hos de nematod-fångande svamparna undersöktes. De flesta svamparna som undersöktes bildade fångstorgan direkt vid sporgroning, och detta var delvis en reaktion på konkurrens om näring med andra mikroorganismer. Vidare var nivån av konkurrens för att utbilda fångstorgan direkt från sporen lägre hos de mer parasitära nematofaga svamparna än för de saprofytiska arterna. (Less)
Abstract
Nematophagous fungi possess various mechanisms for infecting nematodes, and are either obligate parasites or facultative saprophytes. Nematophagous fungi have a potential as biological control agents against plant- and animal-parasitic nematodes. Generally there has been little success in using these fungi in such a way, and one reason might be that too little is known about the ecology of the nematophagous fungi in natural environments. The goal with the work of this thesis was to increase knowledge in this area. The densities and species composition of nematode-trapping fungi were investigated in agricultural soils and in the rhizosphere of crop plants. In root-free soils between 10-1000 propagules of nematode-trapping fungi g1 were... (More)
Nematophagous fungi possess various mechanisms for infecting nematodes, and are either obligate parasites or facultative saprophytes. Nematophagous fungi have a potential as biological control agents against plant- and animal-parasitic nematodes. Generally there has been little success in using these fungi in such a way, and one reason might be that too little is known about the ecology of the nematophagous fungi in natural environments. The goal with the work of this thesis was to increase knowledge in this area. The densities and species composition of nematode-trapping fungi were investigated in agricultural soils and in the rhizosphere of crop plants. In root-free soils between 10-1000 propagules of nematode-trapping fungi g1 were found, and the most common one was Arthrobotrys oligospora. The density of nematode-trapping fungi showed strong seasonal variation, with optima during the late summer and autumn months. Furthermore, their densities were 5-20 times higher in the pea rhizosphere than in the root-free soil. Up to 0.3% of the nematodes were infected with endoparasitic fungi, and the most commonly detected one was Catenaria anguillulae. The relation between naturally occurring nematophagous fungi and nematodes were investigated by making population studies in agricultural soils. The occurrence of the more parasitic nematode-trapping fungi and the endoparasitic fungi both decreased during a three-year study, and at the same time the number of nematodes was reduced by 50%, indicating that a host threshold density exists for the parasitic nematophagous fungi. However, the occurrence of the more saprophytic nematode-trapping fungi was not affected by the decreased number of nematodes, indicating that they are not dependent on nematodes in the soil. Evidence that the nematophagous fungi regulated the number of nematodes in the soil was not obtained in the work of this thesis. For instance, the density of nematode-trapping fungi and the number of nematodes showed similar seasonal dynamics, but were not correlated to each other. Furthermore, compared to the root-free soil the increase of the densities of nematode-trapping fungi in the rhizosphere were not correlated to the increase of the number of nematodes. The transition between the saprophytic and parasitic phase in the nematode-trapping fungi in soil was investigated. Conidial traps were formed in most of the fungi tested, and the formation of conidial traps was partly a response to competition with other microorganisms for nutrients. Furthermore, the degree of competition required to induce conidial-trap formation was lower for more parasitic nematode-trapping fungi than for saprophytic ones. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Jaffee, Bruce, Dept of Nematology, University of California
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Organic farming, Fungistasis, Competition, Bacteria, Conidial traps, Rhizosphere, Seasonal variation, Distribution, Endoparasitic, Nematode, Nematode-trapping, Ecology, Ekologi
pages
104 pages
publisher
Microbial Ecology, Lund University
defense location
Blå salen, Ecology Building, Lund
defense date
1997-03-21 10:15
external identifiers
  • other:ISRN: SE-LUNBDS/NBME­97/1009
ISBN
ISBN 91­7105­083­3
language
English
LU publication?
yes
id
fdb3f25b-9343-4449-be2e-7b1360c9faf2 (old id 29093)
date added to LUP
2007-06-12 14:29:38
date last changed
2016-09-19 08:45:14
@phdthesis{fdb3f25b-9343-4449-be2e-7b1360c9faf2,
  abstract     = {Nematophagous fungi possess various mechanisms for infecting nematodes, and are either obligate parasites or facultative saprophytes. Nematophagous fungi have a potential as biological control agents against plant- and animal-parasitic nematodes. Generally there has been little success in using these fungi in such a way, and one reason might be that too little is known about the ecology of the nematophagous fungi in natural environments. The goal with the work of this thesis was to increase knowledge in this area. The densities and species composition of nematode-trapping fungi were investigated in agricultural soils and in the rhizosphere of crop plants. In root-free soils between 10-1000 propagules of nematode-trapping fungi g1 were found, and the most common one was Arthrobotrys oligospora. The density of nematode-trapping fungi showed strong seasonal variation, with optima during the late summer and autumn months. Furthermore, their densities were 5-20 times higher in the pea rhizosphere than in the root-free soil. Up to 0.3% of the nematodes were infected with endoparasitic fungi, and the most commonly detected one was Catenaria anguillulae. The relation between naturally occurring nematophagous fungi and nematodes were investigated by making population studies in agricultural soils. The occurrence of the more parasitic nematode-trapping fungi and the endoparasitic fungi both decreased during a three-year study, and at the same time the number of nematodes was reduced by 50%, indicating that a host threshold density exists for the parasitic nematophagous fungi. However, the occurrence of the more saprophytic nematode-trapping fungi was not affected by the decreased number of nematodes, indicating that they are not dependent on nematodes in the soil. Evidence that the nematophagous fungi regulated the number of nematodes in the soil was not obtained in the work of this thesis. For instance, the density of nematode-trapping fungi and the number of nematodes showed similar seasonal dynamics, but were not correlated to each other. Furthermore, compared to the root-free soil the increase of the densities of nematode-trapping fungi in the rhizosphere were not correlated to the increase of the number of nematodes. The transition between the saprophytic and parasitic phase in the nematode-trapping fungi in soil was investigated. Conidial traps were formed in most of the fungi tested, and the formation of conidial traps was partly a response to competition with other microorganisms for nutrients. Furthermore, the degree of competition required to induce conidial-trap formation was lower for more parasitic nematode-trapping fungi than for saprophytic ones.},
  author       = {Persmark, Lotta},
  isbn         = {ISBN 91­7105­083­3},
  keyword      = {Organic farming,Fungistasis,Competition,Bacteria,Conidial traps,Rhizosphere,Seasonal variation,Distribution,Endoparasitic,Nematode,Nematode-trapping,Ecology,Ekologi},
  language     = {eng},
  pages        = {104},
  publisher    = {Microbial Ecology, Lund University},
  school       = {Lund University},
  title        = {Ecology of nematophagous fungi in agricultural soils},
  year         = {1997},
}