Risk assessment for microbial antagonists: Are there effects on non-target organisms?

Biological control of phytopathogenic fungi using antagonistic microorganisms is an environmentally friendly alternative in plant protection. However, possible non-target effects of the applied antagonists on ecologically important soil-microbes need to be considered. Therefore, the aim of this study was to analyse the effect of biological control agents (BCAs) on non-target microbes in the field. Whereas the bacterial BCAs Serratia plymuthica HRO-C48 and Streptomyces sp. HRO-71 were applied to control the pathogen Verticillium dahliae on strawberry and potato, the bacterial strains Pseudomonas trivialis 3Re2-7, P fluorescens L13-6-12, S. plymuthica 3Re4-18 and the fungal antagonists Trichoderma reesei G1/8 and T. viride G3/2 were introduced to control Rhizoctonia solani on lettuce and potato. As the analysed BCAs belong to different microbial groups like grampositive (HRO-71) and gramnegative (HRO-C48, L13-6-12, 3Re2-7, 3Re4-18) bacteria or the ascomycota (G1/8, G3/2) and originated from different micro-habitats like the rhizosphere or the endorhiza, general conclusion could be drawn from our results. After BCA treatment we did not observe any long-term effect on the plant-associated microbes in any tested pathosystem. Therefore, no sustainable risks could be seen for the indigenous micro-organisms. Our new findings may help to improve the development as well as the registration procedures of future microbial plant protection products.