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Biological control of plant pathogens on strawberries may be improved by the simultaneous application of different biological control agents (BCAs). Therefore, the compatibility of various BCAs which had previously shown to be effective against powdery mildew (Podosphaera aphanis (Wallr.) U. Braun & S. Takam) under laboratory conditions was examined in vitro. Inhibitory effects between fungal and bacterial BCAs were demonstrated in dual culture tests on two solid nutrient media. Leaf disc assays with single and multiple strain treatments demonstrated either unaffected or significantly improved control of P. aphanis for many multiple strain treatments, even if antagonistic interactions previously occurred in dual culture tests. Highest inhibition of powdery mildew conidiation (80.7% reduction) was achieved with multiple strain treatments with Bacillus subtilis FZB24 and Metarhizium anisopliae (p<0.001). In this combination, conidiation was 3.7 times lower than in single treatments with B. subtilis indicating synergistic interactions between these BCAs. Combinations of Trichoderma harzianum T58 and B. subtilis FZB24 showed antagonistic interactions in dual culture tests as well as in leaf disc assays. In this combination, powdery mildew conidiation on leaf discs was four times higher compared to single treatments with T. harzianum T58.

The increasing use of biological control agents (BCAs) against Botrytis cinerea in strawberry raises the question of whether there are any undesirable impacts of foliar applications of BCAs on nontarget microorganisms in the phyllosphere. Therefore, our objective was to investigate this issue within a field study. Strawberry plants were repeatedly sprayed with three BCAs—namely, RhizoVital 42 fl. (Bacillus amyloliquefaciens FZB42), Trianum-P (Trichoderma harzianum T22), and Naturalis (Beauveria bassiana ATCC 74040)—to suppress Botrytis cinerea infections. Microbial communities of differentially treated leaves were analyzed using plate counts and pyrosequencing and compared with the microbial community of nontreated leaves. Plate count results indicate that the applied Bacillus and Trichoderma spp. survived in the strawberry phyllosphere throughout the strawberry season. However, no significant impacts on the leaf microbiota could be detected by this culture-dependent technique. Pyrosequencing of internal transcribed spacer ribosomal RNA and 16S RNA sequences revealed a change in fungal composition and diversity at class level after the introduction of T. harzianum T22 to the phyllosphere, whereas the bacterial composition and diversity was not affected by either this Trichoderma preparation or the other two BCAs. Our results suggest that pyrosequencing represents a useful method for studying microbial interactions in the phyllosphere.

Ziel der Projektverlängerung war es, die Ergebnisse aus den vorangegangenen Untersuchungen (Projekt: FKZ 06OE354) zum Einsatz von mikrobiologischen Präparaten (BCAs) gegen Graufäule (Botrytis cinerea) und Echten Mehltau (Podospharea aphanis) an ökologisch kultivierten Erdbeeren in einer weiteren Vegetationsperiode abzusichern sowie den Einsatz von mikrobiologischen Präparaten im Integrierten Erdbeeranbau zu erproben. Im Freilandversuch zur Wirkung der BCAs RhizoVital®42 fl. (Bacillus amyloliquefaciens), BoniProtect®forte (Aureobasidium pullulans) und Naturalis® (Beauveria bassiana) gegen Graufäule konnten die vielversprechenden Ergebnisse aus dem Freilandversuch des vorangegangenen Projektes FKZ 06OE354 nicht bestätigt werden. Ergebnisse der Lebendkeimzahlbestimmungen deuten darauf hin, dass die abweichenden Ergebnisse im Projektjahr 2012 auf eine unzureichende Etablierung von A. pullulans zurückzuführen sind. Im Freilandversuch zur Wirkung von ausgewählten BCAs- und BCA-Kombinationen sowie von zusätzlichen BCA-Behandlungen nach einer klassischen Fungizidspritzfolge gegen B. cinerea konnten keinerlei Behandlungseffekte der BCAs RhizoVital®42 fl. und BoniProtect®forte und damit auch keine verbesserten Wirkungen durch deren zusätzlichen Einsatz nach einer Fungizidspritzfolge gegen Graufäule nachgewiesen werden. Ergebnisse der Lebend-keimzahlbestimmungen deuten darauf hin, dass sich A. pullulans im Gegensatz zu B. amyloliquefaciens 2013 nicht in der Erdbeerphyllosphäre etablierte. Ein negativer Effekt der zuvor gespritzten Fungizide auf die BCAs konnte im Versuch nicht detektiert werden. Die Durchführung der 454 Pyrosequenzierung lieferte wertvolle Erkenntnisse über die Struktur von mikrobiellen Gemeinschaften in der Erdbeerphyllosphäre. Die Ergebnisse der 454 Pyrosequenzierung weisen außerdem darauf hin, dass die getesteten BCAs sowie auch die eingesetzten Fungizide die Zusammensetzung von indigenen Pilzgemeinschaften der Erdbeerphyllosphäre beeinflussen können.

Currently, there is little knowledge of the establishment of repeatedly applied biological control agents (BCAs) in the phyllosphere of plants and, in particular, their interactions with the resident microbiome. Under field conditions, the BCA Aureobasidium pullulans was applied as a model organism to organically grown strawberries during two subsequent years (2011, 2012), either as single strain treatment or with the co-application of the entomopathogenic fungus Beauveria bassiana. Fungal and bacterial communities of strawberry leaves were investigated by means of plate counts and 454 pyrosequencing. The establishment of the introduced A. pullulans strains considerably differed between the two years, presumably due to distinct environmental conditions. Short-term and long-term effects of BCA applications on the composition and diversity of fungal communities could be observed as a result of successful establishment of A. pullulans, in 2011, showing, for instance, reduced diversity of fungal communities by competitive displacement shortly after BCA introduction. Due to considerable dynamics in untreated resident microbial communities in the phyllosphere in general, however, we suggest that even the effects caused by the applied BCA preparations in 2011 are negligible under practical conditions.

The aim of this study was to investigate the possible enhancement of leaf decomposition by means of different nitrogen containing products or mulching of leaves and the resulting reduction of the ascopore potential of Venturia inaequalis. For each treatment 30 scabbed leaves of 'Jonagold' were placed in wire-mesh cages with or without fleece to avoid or allow activity of earthworms, respectively. The leaves were treated as follows: untreated as a control, spraying or addition of: urea (46% N), Siapton (organic liquid fertiliser, 7% N), horn meal (organic fertiliser, 10-14% N), Radivit (decomposition enhancer, 9% N) and slightly rotted manure (0,5% N). All treatments were adjusted to a similar amount of N per m2. In addition leaves in one treatment were mulched. The decomposition of leaves was strongly enhanced by mulching and use of Radivit in both years, irrespective of interference by earthworms. Application of urea enhanced decomposition of leaves only in the first year. In tendency, ascospore production was reduced by all treatments in comparison to the control. The lowest number of ascospores was obtained after mulching of leaves in both years. For all other treatments, the influence of the weather and application/distribution technique are discussed.