1
0 10 20 30 40 50 60 70 80 90 Control 25% AP Water 25% F-AP water Mycelium mass (mg) Broth composition AQUAPONIC WATER: A NOVEL SOURCE TO ISOLATE BCAs AGAINST PYTHIUM APHANIDERMATUM? Stouvenakers Gilles, Massart Sébastien, Jijakli M. Haïssam [email protected] Integrated and Urban Plant Pathology Laboratory - Gembloux Agro-Bio Tech - Liege University, Gembloux, Belgium INTRODUCTION RESULTS AND CONCLUSIONS Lettuce root rot in AP A comparison of P. aphanidermatum in vitro mycelium production was made between inoculated broth control (standard V8 CaCO 3 broth) and inoculated V8 CaCO3 broth containing either 25% of AP water or 25% of 0.2 μm filtrated AP (F-AP) water. A very highly significant decrease of mycelium production was observed when 25% of AP water was added. No difference was observed between the control and the broth containing 25% of 0.2 μm filtrated AP water. Based on this test, inhibitory action of AP water seems to be linked to a microbial action. Nevertheless, an indirect action on pathogens by the way of plant stimulation by water compounds cannot be totally excluded. Aquaponic (AP) systems, define as recirculating soilless systems combining aquaculture and hydroponics (HP), are at the core of innovative researches. However, plant pest and more especially plant pathogens management is still unclear. In fact, in this kind of one loop device, where the nutrient plant solution returns to the fish part, chemical pesticides and disinfecting agents are not allowed due to the presence of fishes. Furthermore, they might be toxic for beneficial bacteria present in the system, such as nitrifying bacteria. Among the large possibility of diseases occurring in soilless systems, oomycetes pseudo-fungi, responsible of root rot diseases like Pythium aphanidermatum (Edson) Fitzp, are problematics due to their capacity to produce a mobile form, making the dispersion of the disease easier. Two recent articles put forward the hypothesis of a natural protective action of AP water or fish effluents against plant pathogens during in vitro trials (Gravel et al., 2015; Sirakov et al., 2016). This phenomenon could be linked to the presence of antagonistic microorganisms or inhibitory compounds in fish water. Assumptions that don’t seem aberrant in light of suppressive action already observed in HP systems (Postma et al., 2008). In vitro test Aquaponic lettuces inoculated with P. aphanidermatum mycelium presented significantly less disease symptoms and a better root yields compared with inoculated lettuces grown with HP water adjusted to mineral concentration of AP water. Consequently, suppresssive action of AP water could be considered and potentially linked to antagonistic microorganisms and/or plant defences stimulation. In vivo test Gravel, V. et al., 2015. Fish effluents promote root growth and suppress fungal diseases in tomato transplants. Canadian Journal of Plant Science, 95, pp.427–436. Postma, J., van Os, E. & Bonants, P.J.M., 2008. Ch 10 - Pathogen detection and management strategies in soilless plant growing system. In Soilless Culture: Theory and Practice. Elsevier B.V., pp. 425–457. Sirakov, I. et al., 2016. Potential for combined biocontrol activity against fungal fish and plant pathogens by bacterial isolates from a model aquaponic system. Water, 8, pp.1–7. Mycelium mass depending on the V8 broth content Inhibition of 82% Modality Symptoms scoring (0-6) Fresh root mass (g) Dried root mass (g) Fresh leaf mass (g) Dried leaf mass (g) Inoculated AP 1,00 2,11 0,06 28,16 1,20 Inoculated HP 2,00 * 1,97 0,05 * 27,27 0,97 HP AP In vitro experiments with AP water have been carried out and completed for the first time with in vivo trials to assess its capacity to procure a suppressive action towards P. aphanidermatum. * Significant difference compared to inoculated AP lettuces (AV1 test) *** Very highly significant difference compared to the control (AV1 test) References *** These results highlight that aquaponic water could contribute to find a novel source of BCAs adapted to aquatic environments and able to fight Oomycetes pathogens.
