Evaluation of the Effect of Strigolactones and Synthetic Analogs on Fungi

Strigolactones (SLs) are components of root exudates as a consequence of active release from the roots into 6 the soil. Notably, they have been described as stimulants of seed germination in parasitic plants and of the 7 presymbiotic growth in arbuscular mycorrhizal (AM) fungi, which are a crucial component of the plant root 8 beneficial microbiota. SLs have therefore the potential to influence other microbes that proliferate in the 9 soil around the roots and may interact with plants. A direct effect of SL analogs on the in vitro growth of a 10 number of saprotrophic or plant pathogenic fungi was indeed reported. 11 Here we describe a standardized method to evaluate the effect of SLs or their synthetic analogs on AM 12 and filamentous fungi. For AM fungi, we propose a spore germination assay since it is more straightforward 13 than the hyphal branching assay and it does not require deep expertise and skills. For filamentous fungi that 14 can grow in axenic cultures, we describe the assay based on SLs embedded in the solid medium or dissolved 15 in liquid cultures where the fungus is inoculated to evaluate the effect on growth, hyphal branching or 16 conidia germination. These assays are of help to test the activity of natural SLs as well as of newly designed 17 SL analogs for basic and applied research.