Public Thesis Defense - ELI

Impact of pesticides on arbuscular mycorrhizal fungi with contrasting life history strategies by Victor Hugo RODRIGUEZ MORELOS

Pour l’obtention du grade académique de Doctorat en Sciences agronomiques et Ingénierie biologique

Pesticides are widely used in crops. However, non-target symbiotic microorganisms such as arbuscular mycorrhizal (AM) fungi, may also be affected by these compounds. In this context, the general objective was to study the impact of fungicides (azoxystrobin, pencycuron, flutolanil and fenpropimorph) and the herbicide glyphosate on hyphal healing mechanism (HHM) of Rhizophagus irregularis MUCL 41833 (Glomeraceae) and Gigaspora sp. MUCL 52331 (Gigasporaceae). The anastomosis in intact mycelial networks and dynamics of inorganic phosphorus (Pi) uptake in potato plants were evaluated using R. irregularis. Studies were conducted in vitro and under semi-hydroponic cultivation conditions.

Fungicides at 0.02 and 2 mg L−1 as well as glyphosate at 0.02, 0.2 and 2 mg L−1 impact differentially the HHM. Azoxystrobin at 2 mg L−1 was detrimental to the HHM in both fungi. Glyphosate at 2 mg L−1, stimulated the emission and contact of growing hyphal tips during HHM in R. irregularis, while no impact was noticed in Gigaspora sp. Azoxystrobin and fenpropimorph had a detrimental impact at 2 mg L−1 on the number of anastomoses within and between networks of R. irregularis. Flutolanil and pencycuron did not impact the HHM and anastomosis. Azoxystrobin decreased Pi uptake after 30 days of growth irrespective of the presence of R. irregularis. After 60 days in absence of azoxystrobin, Pi uptake was higher in AM plants, while the reverse was noticed with azoxystrobin.

Our findings suggest that pesticides affect the HHM and anastomosis possibly altering the hyphal tips and may thus affect the capacity of AM fungi to develop mycelial networks in soil. The mechanisms remain to be discovered in view of an integrated management of pesticides without harming AM fungi. The results on Pi uptake tend to support a functional alteration of the symbiosis relative to the cost in terms of nutrients exchanged with the AM fungus based on the availability of nutrients or the demand of Pi by the host plant.

Jury members :

• Prof. Stephan Declerck – Dr. Maryline Calonne (UCLouvain) (Supervisors)
• Prof. Thierry Hance (UCLouvain) (Chairperson)
• Prof. A. Legrève (UCLouvain)
• Prof. Brieuc Hardy (Centre wallon de Recherches agronomiques, Belgique)
• Prof. Anissa Lounes-Hadj Sahraoui (Université du Littoral d’Opale, France)

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