Importance of microbial pest control agents and their metabolites In relation to the natural microbiota on strawberry.

Birgit Jensen, Inge M. B. Knudsen, Dan Funck Jensen, Birgitte Andersen, Kristian Fog Nielsen, Ulf Thrane, John Larsen

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    The main objectives of the this project were to examine the abundance of
    applied microbial pest control agents (MPCAs) and their metabolites
    compared to that of the natural microbiota and to examine the compatibility
    between MPCAs and conventional fungicides and their combination effects in
    disease control.
    A series of laboratory, growth chamber, semi-field and field experiments using
    strawberry as a model plant focusing on commercial microbial pest control
    products (MPCPs) or laboratory MPCAs expected to be on the market within
    10 years served as our experimental platform.
    Initially the background level of indigenous microbial communities and their
    mycotoxins/metabolites on strawberries was examined in a field survey with 4
    conventional and 4 organic growers with different production practise and
    geographic distribution. Culturable bacteria, yeasts and filamentous fungi
    were isolated and identified using both chemotaxonomy (fatty acids and
    metabolite profiling) and morphological characteristics.
    Microbial communities on strawberries were complex including potential
    plant pathogens, opportunistic human pathogens, plant disease biocontrol
    agents and mycotoxin producers. Bacteria were the most abundant and
    diverse group of strawberry microbiota followed by yeasts and filamentous
    fungi. Grower practice did not seem to correlate with the strawberry
    microbiota. Limited difference between microbial communities on
    strawberries from conventional and organic production systems was observed.
    Mycotoxins were not detected in strawberries from any of the 8 different
    growers covering both fresh and worst-case (semi-rotted) berries. However,
    filamentous fungi from the genera Penicillium and Aspergillus isolated from the
    field survey produced high amounts of carcinogenic mycotoxins when applied
    to strawberries in vitro.
    A broad range of microbial biocontrol agents (MPCAs) including the
    commercial Trichoderma based products TRI003, Binab-T and Supresivit and
    the laboratory MPCAs Clonostachys rosea and Ulocladium atrum were
    examined concerning their target and non-target effects, production of
    mycotoxins, fungicide sensitivity and performance (establishment, growth and
    Among the MPCAs tested only the laboratory MPCAs C. rosea and U. atrum
    demonstrated biocontrol effects against the strawberry pathogen Botrytis
    cinerea and the background microbial community was unaffected by both C.
    rosea and U. atrum.
    None of the fungal MPCAs produced any mycotoxins when applied to
    flowers in semi-field and field experiments, but strawberries artificially
    inoculated with Trichoderma-based MPCPs in vitro contained biologically
    active fungal metabolites of the peptaibol family.
    In general, fungicides employed in conventional strawberry production had
    no fungicidal effects on any of the MPCAs. Establishment of Trichoderma
    (TRI003) on berries following flower application was poor and applying
    fungicides prior to the MPCA application did not result in improved MPCA
    In conclusion, the relative importance of deliberately released fungal MPCAs
    and their metabolites in relation to that of the natural strawberry microbiota
    seem to be limited when considering the potential risk from the natural
    microbiota including mycotoxin producers and opportunistic human
    pathogens. In addition, our results suggest that it is possible to combine
    MPCAs and fungicides in an integrated strategy, potentially reducing the
    levels of fungicide applications.
    Original languageEnglish
    PublisherDanish Ministry of the Environment, Environmental Protection Agency
    Number of pages96
    Publication statusPublished - 2011
    SeriesPesticides Research - Report for the Danish EPA
    Number128 2011

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