Seed lots of winter wheat and rye, naturally infested with Microdochium nivale and Fusarium spp., were treated with an isolate of Pseudomonas, which was recovered from roots of Brassica napus. Seeds were treated with bacterial fermentate and dried before sowing or they were directly sprayed in the furrow-opener at the moment of sowing. Besides field experiments, parallel climate chamber bioassays were performed to assess the effect of bacterial treatment on snow mould caused by seed-borne M. nivale and Fusarium spp. The biocontrol effect was assessed by plant density counts and by measuring yield. Significant biocontrol activity, measured by plant density counts, was detected both in field and climate chamber experiments sown with wheat. Biocontrol effect after spray application at sowing was less pronounced, although a slight increase in plant density was observed. The cell concentration required to obtain adequate biocontrol effect was 10 9 CFU per ml for the dose used. The bacterial isolate was identified by 16S rDNA sequencing and biochemical tests as a Pseudomonas brassicacearum strain.
One biocontrol and two plant growth-promoting Pseudomonas spp. isolates were subjected to a safety assessment. Potential risks for human and plant health were investigated and screenings for toxic effects were performed. The antibiotic susceptibility pattern was typical for Pseudomonas and only one of the isolates grew at 37 • C. None of the isolates elicited a hypersensitivity reaction in the tobacco test for plant pathogenicity. For toxicity testing, BACTOX, the Lemna growth bioassay, primary root and shoot growth in vitro and a seed germination/early seedling growth assay were performed. In these assays, one of the plant growth-promoting isolates consistently displayed concentrationdependent adverse effects not seen with the other isolates. Further investigation is needed to determine whether these adverse effects are a concern from a safety assessment perspective, as the identity and mode of action of the active metabolite(s) are unknown. Lack of standardised test procedures for complex samples of microbial origin hampered interpretation of the results from the toxicity assays and there is a need to develop methodology that is more suitable for testing such samples. Nevertheless, the tests employed for the three Pseudomonas isolates were successful in distinguishing isolates with different characteristics. This test framework provides an outline for information collection and safety evaluation when handling new microbial isolates that could be an efficient tool in selecting the best candidate isolates for product development.
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