To use nematophagous fungi for biological control of nematophagous fungi we need to know much more about their biology, on physiological as well as ecological levels. This is especially true for the tri-trophic interactions between the fungi, nematodes, and plant roots. While the invasion of roots by plant-parasitic nematodes is fairly well established, little is known about root colonization by nematophagous fungi. The endophytic growth of these fungi needs to be further investigated using cellular, molecular, as well as ecological studies, to find out if the nematophagous fungi can induce, for instance, systemic resistance in plants to nematodes and other plant pathogens. If this is true and can be developed further, it will add a new property of nematophagous fungi apart from their nematode-destroying ability, and selection of nematophagous fungi for their root colonizing capacity may have equal importance to their nematophagous ability.
Combinations of different types of nematophagous fungi, e.g., egg-parasitic and nematode-trapping fungi, which infect various stages of the nematode life cycles, have been rarely studied in biocontrol experiments. Good egg parasites will be able to destroy nematode eggs, even in root-knot nematode galls inside roots, and nematode trappers may capture juveniles entering or leaving roots. Such experiments need to be conducted in both laboratory and field investigations for development of BCAs as a practical way to control plant-parasitic nematodes.
In the soil and root environment, nematophagous fungi are difficult to study mainly due to lack of appropriate methods. New techniques therefore have been developed and used, especially for tracing fungi in the environment. Antibodies from spore or hyphal surfaces have been tried, but these usually show cross reactions between species and are difficult to use. Molecular techniques probably need to be employed. These could involve, for instance, transformation with marker genes [e.g., the green fluorescence protein (GFP)], or development of molecular beacons or similar approaches based on specific DNA sequences.
Development of proper delivery systems (production, formulation, application, etc.) and the effect on nontarget organisms are key factors involved in the good performance of nematophagous fungi as BCAs. A fair deal of basic research should be invested in these fields. These efforts will also find applications in other fields of root health.
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