Abstract
Biological control of soilborne plant pathogens using beneficial fungi, such as the mycoparasite Trichoderma harzianum, offers the prospect of environmentally benign pest control. However, biocontrol organisms have their own natural enemies; for example the fungivorous nematode Aphelenchoides saprophilus preys on T. harzianum. A trophic cascade occurs when three or more trophic levels are present in a food chain, and consumption of the intermediate species affects biomass or productivity of a lower trophic level; such an interaction in this system might reduce the biocontrol efficacy of T. harzianum. However, the presence of refuges, where intermediate-level species are protected from predation, may reduce the ecological impact of a trophic cascade. Interactions among microscopic organisms in a complex medium such as soil are difficult to observe and quantify. We evaluated the potential of quantitative real-time PCR (qRT-PCR) as a tool to investigate the trophic cascade interaction among T. harzianum, A. saprophilus, and the plant pathogen Sclerotinia sclerotiorum. Results indicate that the mycoparasite colonized and persisted inside structures (sclerotia) of the target plant pathogen, where it was relatively protected from predation compared to the surrounding soil environment. In this way, colonization of sclerotia may provide a refuge that reduces trophic cascade effects in this system. qRT-PCR provided a sensitive method to investigate fungal dynamics over time in this multitrophic system.
Highlights
Reducing chemical pesticide use is a desirable goal for agriculture and forestry
We hypothesized that the Aphelenchoides × Trichoderma × Sclerotinia food chain represents such a trophic cascade, in that fungivory by A. saprophilus reduces the growth of T. harzianum and its ability to successfully colonize sclerotia of S. sclerotiniorum, effectively reducing mycoparasitism of the plant pathogen
We evaluated the potential of quantitative real-time PCR as a tool to investigate a trophic cascade interaction among three species (S. sclerotiorum, T. harzianum, A. saprophilus) in a soil food web, and the ability of T. harzianum to utilize colonized sclerotia as a refuge from predation by the fungivorous nematode
Summary
Reducing chemical pesticide use is a desirable goal for agriculture and forestry. One disease control method, the application of fungi or bacteria as microbial antagonists of plant pathogens, offers prospects of environmentally benign pest control. We hypothesized that the Aphelenchoides × Trichoderma × Sclerotinia food chain represents such a trophic cascade, in that fungivory by A. saprophilus reduces the growth of T. harzianum and its ability to successfully colonize sclerotia of S. sclerotiniorum, effectively reducing mycoparasitism (and reducing biocontrol) of the plant pathogen. We hypothesized that in this way, colonized sclerotia potentially represent a refuge where the biocontrol agent is protected from predation by nematodes, thereby reducing the trophic cascade effect. We evaluated the potential of quantitative real-time PCR (qRT-PCR) as a tool to investigate a trophic cascade interaction among three species (S. sclerotiorum, T. harzianum, A. saprophilus) in a soil food web, and the ability of T. harzianum to utilize colonized sclerotia as a refuge from predation by the fungivorous nematode
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