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item Weaver, Mark

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2005
Publication Date: 12/1/2005
Citation: Weaver, M.A., Kenerley, C. 2005. Density independent population dynamics by trichoderma virens in soil and defined substrates. Biocontrol Science and Technology 15:847-857.

Interpretive Summary: Trichoderma virens is a biocontrol agent that has been deployed for management of soil-borne plant pathogens. It is necessary to develop accurate and ecologically sound models of its growth and establishment in soil. T. virens was found to grow in soil at densities that were not predicted by classical ecology models. At high population densities these models predict that the per capita growth will decrease, but T. virens was shown to have constant per capita growth over a large range of densities. Subsequent experiments with other strains, including a genetically-engineered strains, demonstrated that this phenomena was repeatable in vitro on nutrient-poor media, but not on nutrient-rich media. It was hypothesized that this unique, density independent growth response was linked to the nutrient status of the substrate. This hypothesis was supported in experiments where nutrients were added to soil. With the additional nutrients the soil, which had supported density independent growth, now supported much greater growth that was density dependent. These findings are important in enabling better predictions of the establishment of released biocontrol fungi in nature.

Technical Abstract: Classical models of population dynamics predict that with increasing initial population densities the per capita growth will diminish. Observations over a broad range of initial densities with a wild-type and a genetically engineered strain of the filamentous fungus, Trichoderma virens, in soil and autoclaved soil differed from these predictions. The per capita growth response of T. virens, in vitro, was found to be density dependent on potato dextrose agar, but density independent on water agar. Further experiments with a defined, carbon-free medium (Vogel medium) and with the same medium containing sucrose indicated that density dependent per capita growth occurred in the nutrient-rich medium but not the oligotrophic medium. This hypothesis was tested and supported experimentally through observation of density dependent per capita growth after adding nutrients to autoclaved soil. Development of better models of population dynamics will be important to successfully predict the likelihood and extent of establishment after field release of microorganims.