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

Abstract

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.

Glossary

Allelopathy

a beneficial or detrimental effect from a donor plant to the recipient by chemical pathway (Rice 1984)

Antagonist

an umbrella term for parasites, predators, pathogens, competitors, and other organisms that repel, inhibit, or kill plant parasitic nematodes (Sikora 1992)

Biological control

the action of parasites, predators or pathogens in maintaining another organism’s population density at a lower average than would occur in their absence (Jatala 1986)

Biological control of phytonematode

the reduction in nematode damage by organisms antagonistic towards nematodes through the regulation of nematode populations and/or a reduction in the capacity of nematodes to cause damage, which occurs naturally and is accomplished through the manipulation of environment or by the mass introduction of the antagonist (Sayre and Walter 1991)

Chemical nematicides

the synthetic, not naturally occurring nematicides

Egg-and female-parasitic fungi

those nematophagous fungi capable of parasitising the eggs and females, the sedentary stages in the life cycle of nematode

Endoparasitic fungi

those nematophagous fungi that do not form trapping organs, but use their spores to infect the nematode hosts

Endophytic fungi

endosymbiotic fungi within plant tissues

Mycorrhizal fungi

mycorrhiza is used to describe the symbiotic association between plant roots and fungi; the fungus receives carbohydrates from the plant and in return supplies the plant with nutrients (especially phosphorus) and hormones (Ryan and Jones 2004)

Nematode-suppressive soil

soils in which phytonematodes cannot establish, soils in which they are found but do not cause disease, or soils in which they cause diseases that subsequently diminish with continuous culture of crops (Yin et al. 2003)

Nematode-trapping fungi

those nematophagous fungi with the capacity to capture motile nematodes with specialised trapping organs along the vegetative hyphae

Nematophagous fungi

those fungi with the capacity to capture, parasitise or paralyze nematodes at all stages of their life cycles; they are divided into groups depending on their mode of infection: nematode-trapping, endoparasitic, egg- and female-parasitic, and toxin-producing fungi (Jansson et al. 1997)

Rhizobia

bacteria that display symbiotic interactions with specific legume hosts and nodulate plant roots; rhizobial nodulation is a complex symbiotic process between host plant and rhizobia; the plant provides an energy source and ecological niche for the bacteria and the bacteria provide a source of fixed nitrogen for the plant (Siddiqui and Mahmood 1995)

Rhizosphere

the soil immediately around the root

Toxin-producing fungi

those nematophagous fungi capable of producing nematicidal or nematistatic compounds