A range of specialist and generalist microorganisms in the rhizosphere attacks plant-parasitic nematodes. Plants have a profound effect on the impact of this microflora on the regulation of nematode populations by influencing both the dynamics of the nematode host and the structure and dynamics of the community of antagonists and parasites in the rhizosphere. In general, those organisms that have a saprophytic phase in their life cycle are most affected by environmental conditions in the rhizosphere, but effects on obligate parasites have also been recorded. Although nematodes influence the colonization of roots by pathogenic and beneficial microorganisms, little is known of such interactions with the natural enemies of nematodes in the rhizosphere. As nematodes influence the quantity and quality of root exudates, they are likely to affect the physiology of those microorganisms in the rhizosphere; such changes may be used as signals for nematode antagonists and parasites. Successful biological control strategies will depend on a thorough understanding of these interactions at the population, organismal, and molecular scale.

Rhizosphere interactions and the exploitation of microbial agents for the biological control of plant-parasitic nematodes.

Biological control of plant parasitic nematodes by fungi: A review

Plant-parasitic nematodes cause significant economic losses to a wide variety of crops. Chemical control is a widely used option for plant-parasitic nematode management. However, chemical nematicides are now being reappraised in respect of environmental hazard, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications. This review presents progress made in the field of microbial antagonists of plant-parasitic nematodes, including nematophagous fungi, endophytic fungi, actinomycetes and bacteria. A wide variety of microorganisms are capable of repelling, inhibiting or killing plant-parasitic nematodes, but the commercialisation of these microorganisms lags far behind their resource investigation. One limiting factor is their inconsistent performance in the field. No matter how well suited a nematode antagonist is to a target nematode in a laboratory test, rational management decision can be made only by analysing the interactions naturally occurring among “host plant–nematode target–soil–microbial control agent (MCA)–environment”. As we begin to develop a better understanding of the complex interactions, microbial control of nematodes will be more fine-tuned. Multidisciplinary collaboration and integration of biological control with other control methods will␣also contribute to more successful control practices.

Microbial control of plant-parasitic nematodes: a five-party interaction

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: Pasture plot study with Duddingtonia flagrans

( I ) Endoparasites . 247 ( a ) Encysting spores . 247 (b) Adhesive conidia . . . . . . . . . . . . 248 (c) Ingested conidia . 249 (2) Predators . . . . . . . . . . . . . . . 249 ( a ) Unmodified adhesive hyphae . . . . . . . . . . 252 (b) Adhesive branches . . . . . . . . . . . . 252 (c) Adhesive nets . . . . . . . . . . . . . 253 ( d ) Adhesive knobs . . . . . . . . . . . . . 253 (e) Non-constricting rings . . . . . . . . . . . 254 (f) Constricting rings . . . . . . . . . . . . 255 I11 . Identification . . . . . . . . . . . . . . . 256 ( I ) Taxonomy . . . . . . . . . . . . . . 256 . . . . . . . . . . . . . . . . . . . . . . . .

Nematophagous fungi with particular reference to their ecology

SUMMARY

A study of thirteen species of nematode-trapping Hyphomycetes demonstrated wide differences in their growth rate, competitive saprophytic ability, effect on free-living nematode populations and ability to produce traps spontaneously.



The species producing adhesive reticulate traps tended to have the most rapid growth rates and the highest saprophytic ability ratings. In the soil they appeared to be pre-daceously inefficient and did not form traps in pure culture. In contrast the ring-formers had slow growth rates and lower saprophytic ability ratings. They tended to be predaceously efficient and two of the four species studied formed traps spontaneously. The adhesive branch or knob-forming fungi resembled the ring-formers in their growth rates, predaceous efficiency and spontaneous trap formation.



Thus it appears that the development of predaceous efficiency has been accompanied by a tendency to lose those characters associated with an efficient saprophytic existence in the soil; namely rapid growth rate and good competitive saprophytic ability.

Ecological characteristics of nematode ‐trapping Hyphomycetes

SUMMARY

The decomposition of sucrose in non-sterile soil stimulates an increase in both the population of free-living nematodes and the activity of indigenous nematode-trapping fungi. After sucrose decomposition reaches a certain stage the fungi cease to trap the nematodes still present in the soil. Increasing the amount of sucrose added to the soil stimulates greater increases in nematode population but results in a decrease in predacious activity of the fungi. Experiments using nematode-free soil suggest that the presence of nematodes is necessary to initiate the formation of trapping organs, but that the fungi are incapable of remaining in a predaciously active state in the absence of an organic energy source other than the nematodes. The significance of this is discussed.

The ecology of nematode-trapping fungi in the soil

A direct method of observation has been used to study the behaviour of nematode-destroying fungi during the decomposition of organic matter in the soil. The fungi do not appear to be in a simple equilibrium with populations of free-living nematodes. The nature of this relationship is discussed.

Behaviour of nematode-trapping fungi during decomposition of organic matter in the soil

Ecological characteristics of nematode-trapping Hyphomycetes.: II. Germination of conidia in soil

ATTEMPTS at the biological control of soil-borne eelworm pests have usually involved a process of green manuring or the addition of some organic amendment to the soil1–3. A method has been developed to obtain direct evidence of the effects of such treatments on the predaceous activity of indigenous populations of nematode-trapping fungi in the soil, such work being regarded as fundamental to the investigation of methods using these fungi as agents of biological control.

Roderic C. Cooke

Papers

Ecological characteristics of nematode ‐trapping Hyphomycetes

The ecology of nematode-trapping fungi in the soil

Behaviour of nematode-trapping fungi during decomposition of organic matter in the soil

Ecological characteristics of nematode-trapping Hyphomycetes.: II. Germination of conidia in soil

Agar Disk Method for the Direct Observation of Nematode-trapping Fungi in the Soil