In vivo screening of new biocontrol agents from an aquaponic origin to control Pythium aphanidermatum root rot disease on soilless lettuce

Root diseases in hydroponics are often difficult to control with organic methods. Most authorized biopesticides were not developed for those specific aquatic conditions and lack efficiency. However, it was discovered that some aquaponic systems combining hydroponics and fish farming could have a natural antagonistic effect against the lettuce root pathogen, Pythium aphanidermatum (Stouvenakers et al., 2020). HTS guided microorganisms isolation from aquaponics lettuce roots were carried out. Isolated bacterial and fungal strains were then in vivo screened to control P. aphanidermatum damping-off on lettuce seeds. The 8 most effective strains were then used as treatment to control lettuce seedlings root rot disease caused by the same pathogen in hydroponic conditions. Most of the selected strains had a similar protective effect than a commercial biocontrol agent. More especially, one of our bacterial strains was able to control the pathogen at a better level than the propamocarbe fungicide and the commercial biocontrol agent treatments. For this bacterium, root rot and foliar mass decrease symptoms were significantly reduced and were like the pathogen-free control. These results indicate that aquaponics water can be a source of novel biocontrol agents. Our in vivo methodology seems to be reliable to screen biocontrol agents against the root pathogen. Finally, our tests also highlighted a new antagonistic agent particularly efficient that should be studied and further developed