Potato is a key food security crop worldwide. Under conventional agriculture, this crop is characterized by high levels of fertilizers and pesticides applications which can have detrimental effects on the environment. An alternative or complementary approach to chemicals is the use of beneficial fungal inoculants such as arbuscular mycorrhizal fungi (AMF) or Trichoderma spp. These microorganisms are known to improve plant growth and health and are thus key players in agro-ecosystems. However, their application in the field is complex and results sometimes inconclusive. Consequently, it is important to understand the impacts of agricultural factors on their fitness and functions in the field to guarantee their successful application. In this context, the first objective of the thesis was to study the impact of some fungicides and herbicides on AMF under in vitro culture conditions. Results suggested that fungicides at high concentrations, in particular fungicides with a systemic action, would inhibit growth of the AMF Rhizophagus irregularis. Likewise, systemic herbicides showed a faster and stronger impact on R. irregularis or R. intraradices than chemical or mechanical defoliation. The second objective of the thesis was to identify itineraries for the optimal use of AMF within field systems. Cover crop inoculation with R. irregularis in combination with T. harzianum increased potato yield. Finally, the last objective of the thesis, was to trace native and inoculated R. irregularis within the field by Real-Time quantitative PCR of AMF mitochondrial Large SubUnit (mtLSU). This represent a promising tool to link colonization of the inoculated fungus to the impact observed on plant. Further questions needs to be addressed regarding the ecological and economical significance of the beneficial fungal inoculants under field condition.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201
