Nematode-Antagonistic Fungi

Koon-Hui Wang

University of Florida, Department of Entomology and Nematology, P.O. Box 110620, Gainesville, FL 32611-0620, U.S.A.

(Last updated January, 2002)

Introduction

There are various ways for soil-borne fungi to suppress nematode multiplication. A detailed review of fungi as biocontrol agents against plant-parasitic nematodes has been published (Kerry and Jaffee, 1997). In summary, there are four mechanisms that fungi use to suppress nematodes. Some of these interactions are direct whereas others are indirect. The direct mechanism is performed by 1) fungi that feed on nematodes directly, known as nematophagous fungi; fungi interact with nematodes in an indirect manner by several mechanisms including: 2) fungi that kill nematodes by mycotoxin (Barron and Thorne, 1987) or 3) through the destruction of the feeding sites of sedentary nematodes in roots (Glawe and Stiles, 1989); 4) fungi that are nonpathogenic to plants, but compete with nematodes in roots and significantly reduce nematode multiplication (Sikora, 1992). Many of these fungi are used as potential nematode biocontrol agents; 5) Mycorrhizal fungi improve the growth of nematode infected plants and may also affect nematode development (Hussey and Roncadori, 1982).

This article summarizes groups of nematophagous fungi according to their feeding habits:

A) Nematode-trapping fungi

Facultative fungi that form trapping structure to trap nematodes. There are 6 types of traps reported by Barron (1977).

adhesive hyphae:

eg. Zygomycotina

Stylopage

Cystopage

adhesive traps:

eg. Deuteromycota

Monacrosporium cionopagum (branches)

M. ellipsosporum (knobs)

Arthrobotrys oligospora (networks)

non-adhesive traps

eg. Deuteromycota

Arthrobotrys dactyloides (constricting ring)

(non-constricting ring)

B) Facultative parasitic fungi attacking sedentary stages of nematodes (Kerry and Jaffee, 1997)

These are facultative fungi that are commonly soil saprophytes, and are opportunistic fungi isolated from the sedentary stages (female and egg stages) of sedentary nematodes such as Heterodera, Globodera, and Meloidogyne. They do not form specialized infection structures except appressoria. They can survive and proliferate in soil in the absence of nematodes.

eg. Hyphomycotina

Acremonium

Cylindrocarpon

Fusarium

Paecilomyces

Verticillium

C) Endoparasitic fungi (Kerry and Jaffee, 1997)

These are obligate parasitic fungi that have limited growth in soil outside the colonized nematode cadaver.

They can infect vermiform nematodes by producing adhesive spores attached to cuticle of passing nematodes.

eg. Hyphomycotina

Hirsutella rhossiliensis

Drechmeria coniospora

Verticillium spp.

Some can infect vermiform nematodes by producing conidia spores that can be ingested by nematodes.

Harposporium anguillulae

Some can infect vermiform nematodes by producing motile zoospores that encyst on the nematode’s surface.

eg. Oomycota

Myzocytium spp.

Lagenidium spp.

Chytridiomycota

Catenaria anguillulae

Some can infect sedentary nematodes when the nematodes were exposed on the root surface.

eg. Oomycota

Nematophora gynophila

Further information on nematode biocontrol by nematode-antagonistic fungi can be obtained through:

http://sacs.cpes.peachnet.edu/nemabc/

http://www.area.ba.cnr.it/~e085ac01/bkfair3444.html

http://www.ag.auburn.edu/bci/nematolo.htm

Ecology of Nematode-Trapping and Endoparasitic Fungi (Nematophagous Fungi)

Table 1. Effect of soil edaphic factors on distribution of nematode-antagonistic fungi (Gray, 1985).

Nematophagous fungi	Organic matter	pH	Moisture	Nematode densities
Nematode-trapping	NS^z	low	NS	NS
net	low^y	low	low	NS
ring	high^x	low	high	NS
adhesive hyphae	NS	high	NS	NS
adhesive branch	NS	NS	NS	high
adhesive knobs	NS	low	NS	NS
Endoparasites	high	low	high	high

^zNS =effects of the edaphic factors is not significant.

^ylow=lower value of the edaphic factor is preferred by the group of nematophagous fungi.

^xhigh=higher value of the edaphic factor is preferred by the group of nematophagous fungi.

There are two groups of nematode-trapping fungi (NTF): saprophytic and parasitic NTF (Cooke, 1963).

v Saprophytic NTF—form 3-dimensional-network traps in response to the presence of nematodes. Under low nematode population densities, they remain saprophytic. Therefore, they are regarded as inefficient nematode-trappers.

v Parasitic NTF—have low saprophytic ability, but form traps spontaneously. This group consists of NTF that form constricting rings, adhesive branches and are more effective nematode trappers than the saprophytic NTF (Jasson, 1982).

References

Barron, G. L. 1977. The nematode-destroying fungi, Canadian Biological Publication Ltd.

Barron, G. L., and R. G. Thorne. 1987. Destruction of nematodes species of Pleurotus. Canadian Journal of Botany 65: 774-778.

Cooke, R. C. 1963. Ecological characteristics of nematode-trapping fungi Hyphomycetes. Annual Review of Applied Biology 52: 431-437.

Glawe, D. A., and C. M. Stiles. 1989. Colonization of soybean roots by fungi isolated from cysts of Heterodera glycines. Mycologia 81: 797-799.

Gray, N. F. 1985. Ecology of nematophagous fungi:distribution and habitat. Annual Review of Applied Biology 102: 501-509.

Hussey, R. S., and R. W. Roncadori. 1982. Vesicular-arbuscular mycorrhizae may limit nematode activity and improve plant growth. Plant Disease 66: 9-14.

Jasson, H. B. 1982. Predacity by nematophagous fungi and its relation to the attraction of nematodes. Microbial Ecology 8: 233-240.

Kerry, B. R., and B. A. Jaffee. 1997. Fungi as biological control agents for plant parasitic nematodes. in The Mycota K. Esser and P. A. Lemke, eds., Vol. IV, pp. 204-218. Springer, Verlag Berlin Heidelberg.

Sikora, R. A. 1992. Management of the antagonistic potential in agricultural ecosystems for the biological control of plant parasitic nematodes. Annual Review of Phytopathology 30: 245-247.