Protection of apple and pear flowers against fire blight infections using biocontrol organisms applied via bumble bees

Serge Remy, Bart Cottyn, Jolien Smessaert, Maxime Eeraerts, Miche Claes, Martine Maes, Guy Smagghe, Wannes Keulemans, Olivier Honnay, Hilde Schoofs, Tom Deckers

    Onderzoeksoutput: Bijdrage aan congresC3: Congres - Meeting abstract

    Uittreksel

    During bloom, apple and pear are susceptible to fire blight infection which occurs
    when Erwinia amylovora bacteria colonize the stigma and subsequently reach, due to rain or
    dew droplets, the flower hypanthium where they penetrate the openings of the nectary or
    nectarthodes. First the flowers necrotize then the peduncles, the shoots and finally the
    complete stem. While the disease gradually spreads through the tissues, ooze droplets are
    formed that contain high concentrations of bacteria. In Belgium the infection risk increases
    with increasing temperature making the secondary bloom later in the season more vulnerable
    than the primary bloom in early spring when night temperatures are still low and frost occurs.
    Similarly, trees that are planted late in the season and flower in summer as well as young
    fruits and shoots damaged by hail in the summer can become rapidly infected by
    E. amylovora. This infection is worsened if ooze droplets are present in the orchard. The
    current strategies for control focus on preventive treatments such as sprayings with plant
    defense enhancer molecules like fosethyl aluminium (Aliette®) and laminarin (Vacciplant®) as
    well as with heavy metals including copper and manganese that help to reduce the inoculum
    in the orchard during the season. To avoid phytotoxicity, Aliette® treatments are done before
    and/or after bloom making the use of biocontrol organisms (BCOs) during bloom an attractive
    approach to protect the flowers.
    Although the antagonistic yeast Aureobasidium pullulans (Blossom ProtectTM) that can
    block flower colonization by E. amylovora is registered in Belgium, its use is limited today.
    As flowers gradually open, the BCO should be sprayed at least two to three times during
    bloom to protect all flowers, which is time consuming and expensive. In the research project
    that is presented here, we aim at a continuous application of the BCO at the sites of flower
    infection (i.e. stigma and hypanthium) by bumble bee (Bombus terrestris) vectoring. Besides
    A. pullulans, also existing BCO strains of Bacillus subtilis and Pantoea agglomerans as well
    as a new strain of Paenibacillus polymyxa are tested. A search for new candidate BCOs
    naturally present in apple and pear flower microbiomes is also ongoing. Initial results show
    that (i) under optimal infection conditions there is a risk of E. amylovora spread by bumble
    bees after visiting infected flowers (ii) BCOs are acquired to a variable degree by bumble
    bees, (iii) in 2015 primary bloom flower visitation in the orchard was absent in pear and
    limited in apple, whereas bumble bees have better visited secondary flowers and (iv) tested
    BCOs show potential for fire blight control in the greenhouse
    TaalEngels
    StatusGepubliceerd - 2016
    EvenementIOBC-WPRS, Biological and integrated control of plant pathogens - Berlijn, Duitsland
    Duur: 12-sep-201615-sep-2016

    Congres

    CongresIOBC-WPRS, Biological and integrated control of plant pathogens
    LandDuitsland
    StadBerlijn
    Periode12/09/1615/09/16

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