S14 - Session P4 - Application of aquaponic microorganisms alone or in consortium as original biocontrol method of lettuce root rots in soilless culture

Authors: Iris Szekely *, Gilles Stouvenakers, Sébastien Massart, Haïssam Jijakli

Root pathogens in hydroponic culture are often difficult to control organically. Moreover, most of the available biocontrol agents were not developed for such soilless application and often result in poor efficiency. It is therefore important to find novel sources of beneficial microorganisms that could grow and protect plant root in this kind of aquatic environment. In this context, aquaponic systems that combines hydroponic plant culture and fish farming is a promising source of biocontrol agents. It was shown in a previous study that nutrient water drown from an aquaponic system was able to protect lettuce against root rot disease caused by Pythium aphanidermatum (Stouvenakers et al. , 2020). A list of microorganisms identified by HTS was spotlighted to explain the phenomenon. From this list, selective isolation was undertaken, and 110 strains were obtained. These strains were identified by Sanger sequencing and in vivo screened to control P. aphanidermatum damping-off on lettuce seeds. The efficiency of the 8 best strains was then tested on lettuce seedlings grown hydroponically. Most had a lettuce protective action when applied alone. More especially, 2 bacteria and 1 fungus gave similar or better results than the propamocarbe fungicide control treatment. Based on these findings, next trials will aim at developing a consortium that could give additional or synergetic biocontrol effect by mixing strains depending on their complementarity. Stouvenakers, G. et al. (2020) 'Microbial origin of aquaponic water suppressiveness against Pythium aphanidermatum lettuce root rot disease', Microorganisms , 8(11), pp. 1n25. doi: 10.3390/microorganisms8111683.